1 # Ocean Interpreter - Jamison Creek version
3 Ocean is intended to be a compiled language, so this interpreter is
4 not targeted at being the final product. It is, rather, an intermediate
5 stage and fills that role in two distinct ways.
7 Firstly, it exists as a platform to experiment with the early language
8 design. An interpreter is easy to write and easy to get working, so
9 the barrier for entry is lower if I aim to start with an interpreter.
11 Secondly, the plan for the Ocean compiler is to write it in the
12 [Ocean language](http://ocean-lang.org). To achieve this we naturally
13 need some sort of boot-strap process and this interpreter - written in
14 portable C - will fill that role. It will be used to bootstrap the
17 Two features that are not needed to fill either of these roles are
18 performance and completeness. The interpreter only needs to be fast
19 enough to run small test programs and occasionally to run the compiler
20 on itself. It only needs to be complete enough to test aspects of the
21 design which are developed before the compiler is working, and to run
22 the compiler on itself. Any features not used by the compiler when
23 compiling itself are superfluous. They may be included anyway, but
26 Nonetheless, the interpreter should end up being reasonably complete,
27 and any performance bottlenecks which appear and are easily fixed, will
32 This third version of the interpreter exists to test out some initial
33 ideas relating to types. Particularly it adds arrays (indexed from
34 zero) and simple structures. Basic control flow and variable scoping
35 are already fairly well established, as are basic numerical and
38 Some operators that have only recently been added, and so have not
39 generated all that much experience yet are "and then" and "or else" as
40 short-circuit Boolean operators, and the "if ... else" trinary
41 operator which can select between two expressions based on a third
42 (which appears syntactically in the middle).
44 Elements that are present purely to make a usable language, and
45 without any expectation that they will remain, are the "program'
46 clause, which provides a list of variables to received command-line
47 arguments, and the "print" statement which performs simple output.
49 The current scalar types are "number", "Boolean", and "string".
50 Boolean will likely stay in its current form, the other two might, but
51 could just as easily be changed.
55 Versions of the interpreter which obviously do not support a complete
56 language will be named after creeks and streams. This one is Jamison
59 Once we have something reasonably resembling a complete language, the
60 names of rivers will be used.
61 Early versions of the compiler will be named after seas. Major
62 releases of the compiler will be named after oceans. Hopefully I will
63 be finished once I get to the Pacific Ocean release.
67 As well as parsing and executing a program, the interpreter can print
68 out the program from the parsed internal structure. This is useful
69 for validating the parsing.
70 So the main requirements of the interpreter are:
72 - Parse the program, possibly with tracing,
73 - Analyse the parsed program to ensure consistency,
75 - Execute the program, if no parsing or consistency errors were found.
77 This is all performed by a single C program extracted with
80 There will be two formats for printing the program: a default and one
81 that uses bracketing. So a `--bracket` command line option is needed
82 for that. Normally the first code section found is used, however an
83 alternate section can be requested so that a file (such as this one)
84 can contain multiple programs. This is effected with the `--section`
87 This code must be compiled with `-fplan9-extensions` so that anonymous
88 structures can be used.
90 ###### File: oceani.mk
92 myCFLAGS := -Wall -g -fplan9-extensions
93 CFLAGS := $(filter-out $(myCFLAGS),$(CFLAGS)) $(myCFLAGS)
94 myLDLIBS:= libparser.o libscanner.o libmdcode.o -licuuc
95 LDLIBS := $(filter-out $(myLDLIBS),$(LDLIBS)) $(myLDLIBS)
97 all :: $(LDLIBS) oceani
98 oceani.c oceani.h : oceani.mdc parsergen
99 ./parsergen -o oceani --LALR --tag Parser oceani.mdc
100 oceani.mk: oceani.mdc md2c
103 oceani: oceani.o $(LDLIBS)
104 $(CC) $(CFLAGS) -o oceani oceani.o $(LDLIBS)
106 ###### Parser: header
109 struct parse_context {
110 struct token_config config;
119 #define container_of(ptr, type, member) ({ \
120 const typeof( ((type *)0)->member ) *__mptr = (ptr); \
121 (type *)( (char *)__mptr - offsetof(type,member) );})
123 #define config2context(_conf) container_of(_conf, struct parse_context, \
126 ###### Parser: reduce
127 struct parse_context *c = config2context(config);
135 #include <sys/mman.h>
154 static char Usage[] =
155 "Usage: oceani --trace --print --noexec --brackets --section=SectionName prog.ocn\n";
156 static const struct option long_options[] = {
157 {"trace", 0, NULL, 't'},
158 {"print", 0, NULL, 'p'},
159 {"noexec", 0, NULL, 'n'},
160 {"brackets", 0, NULL, 'b'},
161 {"section", 1, NULL, 's'},
164 const char *options = "tpnbs";
165 int main(int argc, char *argv[])
170 struct section *s, *ss;
171 char *section = NULL;
172 struct parse_context context = {
174 .ignored = (1 << TK_mark),
175 .number_chars = ".,_+- ",
180 int doprint=0, dotrace=0, doexec=1, brackets=0;
182 while ((opt = getopt_long(argc, argv, options, long_options, NULL))
185 case 't': dotrace=1; break;
186 case 'p': doprint=1; break;
187 case 'n': doexec=0; break;
188 case 'b': brackets=1; break;
189 case 's': section = optarg; break;
190 default: fprintf(stderr, Usage);
194 if (optind >= argc) {
195 fprintf(stderr, "oceani: no input file given\n");
198 fd = open(argv[optind], O_RDONLY);
200 fprintf(stderr, "oceani: cannot open %s\n", argv[optind]);
203 context.file_name = argv[optind];
204 len = lseek(fd, 0, 2);
205 file = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
206 s = code_extract(file, file+len, NULL);
208 fprintf(stderr, "oceani: could not find any code in %s\n",
213 ## context initialization
216 for (ss = s; ss; ss = ss->next) {
217 struct text sec = ss->section;
218 if (sec.len == strlen(section) &&
219 strncmp(sec.txt, section, sec.len) == 0)
223 fprintf(stderr, "oceani: cannot find section %s\n",
229 parse_oceani(ss->code, &context.config, dotrace ? stderr : NULL);
232 fprintf(stderr, "oceani: no program found.\n");
233 context.parse_error = 1;
235 if (context.prog && doprint) {
238 print_exec(context.prog, 0, brackets);
240 if (context.prog && doexec && !context.parse_error) {
241 if (!analyse_prog(context.prog, &context)) {
242 fprintf(stderr, "oceani: type error in program - not running.\n");
245 interp_prog(context.prog, argv+optind+1);
247 free_exec(context.prog);
250 struct section *t = s->next;
256 ## free context types
257 exit(context.parse_error ? 1 : 0);
262 The four requirements of parse, analyse, print, interpret apply to
263 each language element individually so that is how most of the code
266 Three of the four are fairly self explanatory. The one that requires
267 a little explanation is the analysis step.
269 The current language design does not require the types of variables to
270 be declared, but they must still have a single type. Different
271 operations impose different requirements on the variables, for example
272 addition requires both arguments to be numeric, and assignment
273 requires the variable on the left to have the same type as the
274 expression on the right.
276 Analysis involves propagating these type requirements around and
277 consequently setting the type of each variable. If any requirements
278 are violated (e.g. a string is compared with a number) or if a
279 variable needs to have two different types, then an error is raised
280 and the program will not run.
282 If the same variable is declared in both branchs of an 'if/else', or
283 in all cases of a 'switch' then the multiple instances may be merged
284 into just one variable if the variable is referenced after the
285 conditional statement. When this happens, the types must naturally be
286 consistent across all the branches. When the variable is not used
287 outside the if, the variables in the different branches are distinct
288 and can be of different types.
290 Undeclared names may only appear in "use" statements and "case" expressions.
291 These names are given a type of "label" and a unique value.
292 This allows them to fill the role of a name in an enumerated type, which
293 is useful for testing the `switch` statement.
295 As we will see, the condition part of a `while` statement can return
296 either a Boolean or some other type. This requires that the expected
297 type that gets passed around comprises a type and a flag to indicate
298 that `Tbool` is also permitted.
300 As there are, as yet, no distinct types that are compatible, there
301 isn't much subtlety in the analysis. When we have distinct number
302 types, this will become more interesting.
306 When analysis discovers an inconsistency it needs to report an error;
307 just refusing to run the code ensures that the error doesn't cascade,
308 but by itself it isn't very useful. A clear understanding of the sort
309 of error message that are useful will help guide the process of
312 At a simplistic level, the only sort of error that type analysis can
313 report is that the type of some construct doesn't match a contextual
314 requirement. For example, in `4 + "hello"` the addition provides a
315 contextual requirement for numbers, but `"hello"` is not a number. In
316 this particular example no further information is needed as the types
317 are obvious from local information. When a variable is involved that
318 isn't the case. It may be helpful to explain why the variable has a
319 particular type, by indicating the location where the type was set,
320 whether by declaration or usage.
322 Using a recursive-descent analysis we can easily detect a problem at
323 multiple locations. In "`hello:= "there"; 4 + hello`" the addition
324 will detect that one argument is not a number and the usage of `hello`
325 will detect that a number was wanted, but not provided. In this
326 (early) version of the language, we will generate error reports at
327 multiple locations, so the use of `hello` will report an error and
328 explain were the value was set, and the addition will report an error
329 and say why numbers are needed. To be able to report locations for
330 errors, each language element will need to record a file location
331 (line and column) and each variable will need to record the language
332 element where its type was set. For now we will assume that each line
333 of an error message indicates one location in the file, and up to 2
334 types. So we provide a `printf`-like function which takes a format, a
335 location (a `struct exec` which has not yet been introduced), and 2
336 types. "`%1`" reports the first type, "`%2`" reports the second. We
337 will need a function to print the location, once we know how that is
338 stored. e As will be explained later, there are sometimes extra rules for
339 type matching and they might affect error messages, we need to pass those
342 As well as type errors, we sometimes need to report problems with
343 tokens, which might be unexpected or might name a type that has not
344 been defined. For these we have `tok_err()` which reports an error
345 with a given token. Each of the error functions sets the flag in the
346 context so indicate that parsing failed.
350 static void fput_loc(struct exec *loc, FILE *f);
352 ###### core functions
354 static void type_err(struct parse_context *c,
355 char *fmt, struct exec *loc,
356 struct type *t1, int rules, struct type *t2)
358 fprintf(stderr, "%s:", c->file_name);
359 fput_loc(loc, stderr);
360 for (; *fmt ; fmt++) {
367 case '%': fputc(*fmt, stderr); break; // NOTEST
368 default: fputc('?', stderr); break; // NOTEST
370 type_print(t1, stderr);
373 type_print(t2, stderr);
382 static void tok_err(struct parse_context *c, char *fmt, struct token *t)
384 fprintf(stderr, "%s:%d:%d: %s: %.*s\n", c->file_name, t->line, t->col, fmt,
385 t->txt.len, t->txt.txt);
389 ## Entities: declared and predeclared.
391 There are various "things" that the language and/or the interpreter
392 needs to know about to parse and execute a program. These include
393 types, variables, values, and executable code. These are all lumped
394 together under the term "entities" (calling them "objects" would be
395 confusing) and introduced here. The following section will present the
396 different specific code elements which comprise or manipulate these
401 Values come in a wide range of types, with more likely to be added.
402 Each type needs to be able to print its own values (for convenience at
403 least) as well as to compare two values, at least for equality and
404 possibly for order. For now, values might need to be duplicated and
405 freed, though eventually such manipulations will be better integrated
408 Rather than requiring every numeric type to support all numeric
409 operations (add, multiple, etc), we allow types to be able to present
410 as one of a few standard types: integer, float, and fraction. The
411 existence of these conversion functions eventually enable types to
412 determine if they are compatible with other types, though such types
413 have not yet been implemented.
415 Named type are stored in a simple linked list. Objects of each type are
416 "values" which are often passed around by value.
423 ## value union fields
431 void (*init)(struct type *type, struct value *val);
432 void (*prepare_type)(struct type *type);
433 void (*print)(struct type *type, struct value *val);
434 void (*print_type)(struct type *type, FILE *f);
435 int (*cmp_order)(struct type *t1, struct type *t2,
436 struct value *v1, struct value *v2);
437 int (*cmp_eq)(struct type *t1, struct type *t2,
438 struct value *v1, struct value *v2);
439 void (*dup)(struct type *type, struct value *vold, struct value *vnew);
440 void (*free)(struct type *type, struct value *val);
441 void (*free_type)(struct type *t);
442 long long (*to_int)(struct value *v);
443 double (*to_float)(struct value *v);
444 int (*to_mpq)(mpq_t *q, struct value *v);
453 struct type *typelist;
457 static struct type *find_type(struct parse_context *c, struct text s)
459 struct type *l = c->typelist;
462 text_cmp(l->name, s) != 0)
467 static struct type *add_type(struct parse_context *c, struct text s,
472 n = calloc(1, sizeof(*n));
475 n->next = c->typelist;
480 static void free_type(struct type *t)
482 /* The type is always a reference to something in the
483 * context, so we don't need to free anything.
487 static void free_value(struct type *type, struct value *v)
493 static void type_print(struct type *type, FILE *f)
496 fputs("*unknown*type*", f);
497 else if (type->name.len)
498 fprintf(f, "%.*s", type->name.len, type->name.txt);
499 else if (type->print_type)
500 type->print_type(type, f);
502 fputs("*invalid*type*", f); // NOTEST
505 static void val_init(struct type *type, struct value *val)
507 if (type && type->init)
508 type->init(type, val);
511 static void dup_value(struct type *type,
512 struct value *vold, struct value *vnew)
514 if (type && type->dup)
515 type->dup(type, vold, vnew);
518 static int value_cmp(struct type *tl, struct type *tr,
519 struct value *left, struct value *right)
521 if (tl && tl->cmp_order)
522 return tl->cmp_order(tl, tr, left, right);
523 if (tl && tl->cmp_eq)
524 return tl->cmp_eq(tl, tr, left, right);
528 static void print_value(struct type *type, struct value *v)
530 if (type && type->print)
531 type->print(type, v);
533 printf("*Unknown*"); // NOTEST
536 static struct value *val_alloc(struct type *t, struct value *init)
543 ret = calloc(1, t->size);
545 memcpy(ret, init, t->size);
553 static void free_value(struct type *type, struct value *v);
554 static int type_compat(struct type *require, struct type *have, int rules);
555 static void type_print(struct type *type, FILE *f);
556 static void val_init(struct type *type, struct value *v);
557 static void dup_value(struct type *type,
558 struct value *vold, struct value *vnew);
559 static int value_cmp(struct type *tl, struct type *tr,
560 struct value *left, struct value *right);
561 static void print_value(struct type *type, struct value *v);
563 ###### free context types
565 while (context.typelist) {
566 struct type *t = context.typelist;
568 context.typelist = t->next;
576 Values of the base types can be numbers, which we represent as
577 multi-precision fractions, strings, Booleans and labels. When
578 analysing the program we also need to allow for places where no value
579 is meaningful (type `Tnone`) and where we don't know what type to
580 expect yet (type is `NULL`).
582 Values are never shared, they are always copied when used, and freed
583 when no longer needed.
585 When propagating type information around the program, we need to
586 determine if two types are compatible, where type `NULL` is compatible
587 with anything. There are two special cases with type compatibility,
588 both related to the Conditional Statement which will be described
589 later. In some cases a Boolean can be accepted as well as some other
590 primary type, and in others any type is acceptable except a label (`Vlabel`).
591 A separate function encoding these cases will simplify some code later.
595 int (*compat)(struct type *this, struct type *other);
599 static int type_compat(struct type *require, struct type *have, int rules)
601 if ((rules & Rboolok) && have == Tbool)
603 if ((rules & Rnolabel) && have == Tlabel)
605 if (!require || !have)
609 return require->compat(require, have);
611 return require == have;
616 #include "parse_string.h"
617 #include "parse_number.h"
620 myLDLIBS := libnumber.o libstring.o -lgmp
621 LDLIBS := $(filter-out $(myLDLIBS),$(LDLIBS)) $(myLDLIBS)
623 ###### type union fields
624 enum vtype {Vnone, Vstr, Vnum, Vbool, Vlabel} vtype;
626 ###### value union fields
633 static void _free_value(struct type *type, struct value *v)
637 switch (type->vtype) {
639 case Vstr: free(v->str.txt); break;
640 case Vnum: mpq_clear(v->num); break;
646 ###### value functions
648 static void _val_init(struct type *type, struct value *val)
650 switch(type->vtype) {
651 case Vnone: // NOTEST
654 mpq_init(val->num); break;
656 val->str.txt = malloc(1);
662 case Vlabel: // NOTEST
663 val->label = NULL; // NOTEST
668 static void _dup_value(struct type *type,
669 struct value *vold, struct value *vnew)
671 switch (type->vtype) {
672 case Vnone: // NOTEST
675 vnew->label = vold->label;
678 vnew->bool = vold->bool;
682 mpq_set(vnew->num, vold->num);
685 vnew->str.len = vold->str.len;
686 vnew->str.txt = malloc(vnew->str.len);
687 memcpy(vnew->str.txt, vold->str.txt, vnew->str.len);
692 static int _value_cmp(struct type *tl, struct type *tr,
693 struct value *left, struct value *right)
697 return tl - tr; // NOTEST
699 case Vlabel: cmp = left->label == right->label ? 0 : 1; break;
700 case Vnum: cmp = mpq_cmp(left->num, right->num); break;
701 case Vstr: cmp = text_cmp(left->str, right->str); break;
702 case Vbool: cmp = left->bool - right->bool; break;
703 case Vnone: cmp = 0; // NOTEST
708 static void _print_value(struct type *type, struct value *v)
710 switch (type->vtype) {
711 case Vnone: // NOTEST
712 printf("*no-value*"); break; // NOTEST
713 case Vlabel: // NOTEST
714 printf("*label-%p*", v->label); break; // NOTEST
716 printf("%.*s", v->str.len, v->str.txt); break;
718 printf("%s", v->bool ? "True":"False"); break;
723 mpf_set_q(fl, v->num);
724 gmp_printf("%Fg", fl);
731 static void _free_value(struct type *type, struct value *v);
733 static struct type base_prototype = {
735 .print = _print_value,
736 .cmp_order = _value_cmp,
737 .cmp_eq = _value_cmp,
742 static struct type *Tbool, *Tstr, *Tnum, *Tnone, *Tlabel;
745 static struct type *add_base_type(struct parse_context *c, char *n,
746 enum vtype vt, int size)
748 struct text txt = { n, strlen(n) };
751 t = add_type(c, txt, &base_prototype);
754 t->align = size > sizeof(void*) ? sizeof(void*) : size;
755 if (t->size & (t->align - 1))
756 t->size = (t->size | (t->align - 1)) + 1;
760 ###### context initialization
762 Tbool = add_base_type(&context, "Boolean", Vbool, sizeof(char));
763 Tstr = add_base_type(&context, "string", Vstr, sizeof(struct text));
764 Tnum = add_base_type(&context, "number", Vnum, sizeof(mpq_t));
765 Tnone = add_base_type(&context, "none", Vnone, 0);
766 Tlabel = add_base_type(&context, "label", Vlabel, sizeof(void*));
770 Variables are scoped named values. We store the names in a linked list
771 of "bindings" sorted in lexical order, and use sequential search and
778 struct binding *next; // in lexical order
782 This linked list is stored in the parse context so that "reduce"
783 functions can find or add variables, and so the analysis phase can
784 ensure that every variable gets a type.
788 struct binding *varlist; // In lexical order
792 static struct binding *find_binding(struct parse_context *c, struct text s)
794 struct binding **l = &c->varlist;
799 (cmp = text_cmp((*l)->name, s)) < 0)
803 n = calloc(1, sizeof(*n));
810 Each name can be linked to multiple variables defined in different
811 scopes. Each scope starts where the name is declared and continues
812 until the end of the containing code block. Scopes of a given name
813 cannot nest, so a declaration while a name is in-scope is an error.
815 ###### binding fields
816 struct variable *var;
820 struct variable *previous;
823 struct binding *name;
824 struct exec *where_decl;// where name was declared
825 struct exec *where_set; // where type was set
829 While the naming seems strange, we include local constants in the
830 definition of variables. A name declared `var := value` can
831 subsequently be changed, but a name declared `var ::= value` cannot -
834 ###### variable fields
837 Scopes in parallel branches can be partially merged. More
838 specifically, if a given name is declared in both branches of an
839 if/else then its scope is a candidate for merging. Similarly if
840 every branch of an exhaustive switch (e.g. has an "else" clause)
841 declares a given name, then the scopes from the branches are
842 candidates for merging.
844 Note that names declared inside a loop (which is only parallel to
845 itself) are never visible after the loop. Similarly names defined in
846 scopes which are not parallel, such as those started by `for` and
847 `switch`, are never visible after the scope. Only variables defined in
848 both `then` and `else` (including the implicit then after an `if`, and
849 excluding `then` used with `for`) and in all `case`s and `else` of a
850 `switch` or `while` can be visible beyond the `if`/`switch`/`while`.
852 Labels, which are a bit like variables, follow different rules.
853 Labels are not explicitly declared, but if an undeclared name appears
854 in a context where a label is legal, that effectively declares the
855 name as a label. The declaration remains in force (or in scope) at
856 least to the end of the immediately containing block and conditionally
857 in any larger containing block which does not declare the name in some
858 other way. Importantly, the conditional scope extension happens even
859 if the label is only used in one parallel branch of a conditional --
860 when used in one branch it is treated as having been declared in all
863 Merge candidates are tentatively visible beyond the end of the
864 branching statement which creates them. If the name is used, the
865 merge is affirmed and they become a single variable visible at the
866 outer layer. If not - if it is redeclared first - the merge lapses.
868 To track scopes we have an extra stack, implemented as a linked list,
869 which roughly parallels the parse stack and which is used exclusively
870 for scoping. When a new scope is opened, a new frame is pushed and
871 the child-count of the parent frame is incremented. This child-count
872 is used to distinguish between the first of a set of parallel scopes,
873 in which declared variables must not be in scope, and subsequent
874 branches, whether they may already be conditionally scoped.
876 To push a new frame *before* any code in the frame is parsed, we need a
877 grammar reduction. This is most easily achieved with a grammar
878 element which derives the empty string, and creates the new scope when
879 it is recognised. This can be placed, for example, between a keyword
880 like "if" and the code following it.
884 struct scope *parent;
890 struct scope *scope_stack;
893 static void scope_pop(struct parse_context *c)
895 struct scope *s = c->scope_stack;
897 c->scope_stack = s->parent;
902 static void scope_push(struct parse_context *c)
904 struct scope *s = calloc(1, sizeof(*s));
906 c->scope_stack->child_count += 1;
907 s->parent = c->scope_stack;
915 OpenScope -> ${ scope_push(c); }$
916 ClosePara -> ${ var_block_close(c, CloseParallel); }$
918 Each variable records a scope depth and is in one of four states:
920 - "in scope". This is the case between the declaration of the
921 variable and the end of the containing block, and also between
922 the usage with affirms a merge and the end of that block.
924 The scope depth is not greater than the current parse context scope
925 nest depth. When the block of that depth closes, the state will
926 change. To achieve this, all "in scope" variables are linked
927 together as a stack in nesting order.
929 - "pending". The "in scope" block has closed, but other parallel
930 scopes are still being processed. So far, every parallel block at
931 the same level that has closed has declared the name.
933 The scope depth is the depth of the last parallel block that
934 enclosed the declaration, and that has closed.
936 - "conditionally in scope". The "in scope" block and all parallel
937 scopes have closed, and no further mention of the name has been
938 seen. This state includes a secondary nest depth which records the
939 outermost scope seen since the variable became conditionally in
940 scope. If a use of the name is found, the variable becomes "in
941 scope" and that secondary depth becomes the recorded scope depth.
942 If the name is declared as a new variable, the old variable becomes
943 "out of scope" and the recorded scope depth stays unchanged.
945 - "out of scope". The variable is neither in scope nor conditionally
946 in scope. It is permanently out of scope now and can be removed from
947 the "in scope" stack.
949 ###### variable fields
950 int depth, min_depth;
951 enum { OutScope, PendingScope, CondScope, InScope } scope;
952 struct variable *in_scope;
956 struct variable *in_scope;
958 All variables with the same name are linked together using the
959 'previous' link. Those variable that have been affirmatively merged all
960 have a 'merged' pointer that points to one primary variable - the most
961 recently declared instance. When merging variables, we need to also
962 adjust the 'merged' pointer on any other variables that had previously
963 been merged with the one that will no longer be primary.
965 A variable that is no longer the most recent instance of a name may
966 still have "pending" scope, if it might still be merged with most
967 recent instance. These variables don't really belong in the
968 "in_scope" list, but are not immediately removed when a new instance
969 is found. Instead, they are detected and ignored when considering the
970 list of in_scope names.
972 ###### variable fields
973 struct variable *merged;
977 static void variable_merge(struct variable *primary, struct variable *secondary)
983 primary = primary->merged;
985 for (v = primary->previous; v; v=v->previous)
986 if (v == secondary || v == secondary->merged ||
987 v->merged == secondary ||
988 (v->merged && v->merged == secondary->merged)) {
994 ###### free context vars
996 while (context.varlist) {
997 struct binding *b = context.varlist;
998 struct variable *v = b->var;
999 context.varlist = b->next;
1002 struct variable *t = v;
1005 free_value(t->type, t->val);
1008 // This is a global constant
1009 free_exec(t->where_decl);
1014 #### Manipulating Bindings
1016 When a name is conditionally visible, a new declaration discards the
1017 old binding - the condition lapses. Conversely a usage of the name
1018 affirms the visibility and extends it to the end of the containing
1019 block - i.e. the block that contains both the original declaration and
1020 the latest usage. This is determined from `min_depth`. When a
1021 conditionally visible variable gets affirmed like this, it is also
1022 merged with other conditionally visible variables with the same name.
1024 When we parse a variable declaration we either report an error if the
1025 name is currently bound, or create a new variable at the current nest
1026 depth if the name is unbound or bound to a conditionally scoped or
1027 pending-scope variable. If the previous variable was conditionally
1028 scoped, it and its homonyms becomes out-of-scope.
1030 When we parse a variable reference (including non-declarative assignment
1031 "foo = bar") we report an error if the name is not bound or is bound to
1032 a pending-scope variable; update the scope if the name is bound to a
1033 conditionally scoped variable; or just proceed normally if the named
1034 variable is in scope.
1036 When we exit a scope, any variables bound at this level are either
1037 marked out of scope or pending-scoped, depending on whether the scope
1038 was sequential or parallel. Here a "parallel" scope means the "then"
1039 or "else" part of a conditional, or any "case" or "else" branch of a
1040 switch. Other scopes are "sequential".
1042 When exiting a parallel scope we check if there are any variables that
1043 were previously pending and are still visible. If there are, then
1044 there weren't redeclared in the most recent scope, so they cannot be
1045 merged and must become out-of-scope. If it is not the first of
1046 parallel scopes (based on `child_count`), we check that there was a
1047 previous binding that is still pending-scope. If there isn't, the new
1048 variable must now be out-of-scope.
1050 When exiting a sequential scope that immediately enclosed parallel
1051 scopes, we need to resolve any pending-scope variables. If there was
1052 no `else` clause, and we cannot determine that the `switch` was exhaustive,
1053 we need to mark all pending-scope variable as out-of-scope. Otherwise
1054 all pending-scope variables become conditionally scoped.
1057 enum closetype { CloseSequential, CloseParallel, CloseElse };
1059 ###### ast functions
1061 static struct variable *var_decl(struct parse_context *c, struct text s)
1063 struct binding *b = find_binding(c, s);
1064 struct variable *v = b->var;
1066 switch (v ? v->scope : OutScope) {
1068 /* Caller will report the error */
1072 v && v->scope == CondScope;
1074 v->scope = OutScope;
1078 v = calloc(1, sizeof(*v));
1079 v->previous = b->var;
1082 v->min_depth = v->depth = c->scope_depth;
1084 v->in_scope = c->in_scope;
1090 static struct variable *var_ref(struct parse_context *c, struct text s)
1092 struct binding *b = find_binding(c, s);
1093 struct variable *v = b->var;
1094 struct variable *v2;
1096 switch (v ? v->scope : OutScope) {
1099 /* Caller will report the error */
1102 /* All CondScope variables of this name need to be merged
1103 * and become InScope
1105 v->depth = v->min_depth;
1107 for (v2 = v->previous;
1108 v2 && v2->scope == CondScope;
1110 variable_merge(v, v2);
1118 static void var_block_close(struct parse_context *c, enum closetype ct)
1120 /* Close off all variables that are in_scope */
1121 struct variable *v, **vp, *v2;
1124 for (vp = &c->in_scope;
1125 v = *vp, v && v->depth > c->scope_depth && v->min_depth > c->scope_depth;
1127 if (v->name->var == v) switch (ct) {
1129 case CloseParallel: /* handle PendingScope */
1133 if (c->scope_stack->child_count == 1)
1134 v->scope = PendingScope;
1135 else if (v->previous &&
1136 v->previous->scope == PendingScope)
1137 v->scope = PendingScope;
1138 else if (v->type == Tlabel)
1139 v->scope = PendingScope;
1140 else if (v->name->var == v)
1141 v->scope = OutScope;
1142 if (ct == CloseElse) {
1143 /* All Pending variables with this name
1144 * are now Conditional */
1146 v2 && v2->scope == PendingScope;
1148 v2->scope = CondScope;
1153 v2 && v2->scope == PendingScope;
1155 if (v2->type != Tlabel)
1156 v2->scope = OutScope;
1158 case OutScope: break;
1161 case CloseSequential:
1162 if (v->type == Tlabel)
1163 v->scope = PendingScope;
1166 v->scope = OutScope;
1169 /* There was no 'else', so we can only become
1170 * conditional if we know the cases were exhaustive,
1171 * and that doesn't mean anything yet.
1172 * So only labels become conditional..
1175 v2 && v2->scope == PendingScope;
1177 if (v2->type == Tlabel) {
1178 v2->scope = CondScope;
1179 v2->min_depth = c->scope_depth;
1181 v2->scope = OutScope;
1184 case OutScope: break;
1188 if (v->scope == OutScope || v->name->var != v)
1197 Executables can be lots of different things. In many cases an
1198 executable is just an operation combined with one or two other
1199 executables. This allows for expressions and lists etc. Other times an
1200 executable is something quite specific like a constant or variable name.
1201 So we define a `struct exec` to be a general executable with a type, and
1202 a `struct binode` which is a subclass of `exec`, forms a node in a
1203 binary tree, and holds an operation. There will be other subclasses,
1204 and to access these we need to be able to `cast` the `exec` into the
1205 various other types. The first field in any `struct exec` is the type
1206 from the `exec_types` enum.
1209 #define cast(structname, pointer) ({ \
1210 const typeof( ((struct structname *)0)->type) *__mptr = &(pointer)->type; \
1211 if (__mptr && *__mptr != X##structname) abort(); \
1212 (struct structname *)( (char *)__mptr);})
1214 #define new(structname) ({ \
1215 struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
1216 __ptr->type = X##structname; \
1217 __ptr->line = -1; __ptr->column = -1; \
1220 #define new_pos(structname, token) ({ \
1221 struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
1222 __ptr->type = X##structname; \
1223 __ptr->line = token.line; __ptr->column = token.col; \
1232 enum exec_types type;
1240 struct exec *left, *right;
1243 ###### ast functions
1245 static int __fput_loc(struct exec *loc, FILE *f)
1249 if (loc->line >= 0) {
1250 fprintf(f, "%d:%d: ", loc->line, loc->column);
1253 if (loc->type == Xbinode)
1254 return __fput_loc(cast(binode,loc)->left, f) ||
1255 __fput_loc(cast(binode,loc)->right, f);
1258 static void fput_loc(struct exec *loc, FILE *f)
1260 if (!__fput_loc(loc, f))
1261 fprintf(f, "??:??: "); // NOTEST
1264 Each different type of `exec` node needs a number of functions defined,
1265 a bit like methods. We must be able to free it, print it, analyse it
1266 and execute it. Once we have specific `exec` types we will need to
1267 parse them too. Let's take this a bit more slowly.
1271 The parser generator requires a `free_foo` function for each struct
1272 that stores attributes and they will often be `exec`s and subtypes
1273 there-of. So we need `free_exec` which can handle all the subtypes,
1274 and we need `free_binode`.
1276 ###### ast functions
1278 static void free_binode(struct binode *b)
1283 free_exec(b->right);
1287 ###### core functions
1288 static void free_exec(struct exec *e)
1297 ###### forward decls
1299 static void free_exec(struct exec *e);
1301 ###### free exec cases
1302 case Xbinode: free_binode(cast(binode, e)); break;
1306 Printing an `exec` requires that we know the current indent level for
1307 printing line-oriented components. As will become clear later, we
1308 also want to know what sort of bracketing to use.
1310 ###### ast functions
1312 static void do_indent(int i, char *str)
1319 ###### core functions
1320 static void print_binode(struct binode *b, int indent, int bracket)
1324 ## print binode cases
1328 static void print_exec(struct exec *e, int indent, int bracket)
1334 print_binode(cast(binode, e), indent, bracket); break;
1339 ###### forward decls
1341 static void print_exec(struct exec *e, int indent, int bracket);
1345 As discussed, analysis involves propagating type requirements around the
1346 program and looking for errors.
1348 So `propagate_types` is passed an expected type (being a `struct type`
1349 pointer together with some `val_rules` flags) that the `exec` is
1350 expected to return, and returns the type that it does return, either
1351 of which can be `NULL` signifying "unknown". An `ok` flag is passed
1352 by reference. It is set to `0` when an error is found, and `2` when
1353 any change is made. If it remains unchanged at `1`, then no more
1354 propagation is needed.
1358 enum val_rules {Rnolabel = 1<<0, Rboolok = 1<<1, Rnoconstant = 2<<1};
1362 if (rules & Rnolabel)
1363 fputs(" (labels not permitted)", stderr);
1366 ###### core functions
1368 static struct type *propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1369 struct type *type, int rules);
1370 static struct type *__propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1371 struct type *type, int rules)
1378 switch (prog->type) {
1381 struct binode *b = cast(binode, prog);
1383 ## propagate binode cases
1387 ## propagate exec cases
1392 static struct type *propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1393 struct type *type, int rules)
1395 struct type *ret = __propagate_types(prog, c, ok, type, rules);
1404 Interpreting an `exec` doesn't require anything but the `exec`. State
1405 is stored in variables and each variable will be directly linked from
1406 within the `exec` tree. The exception to this is the whole `program`
1407 which needs to look at command line arguments. The `program` will be
1408 interpreted separately.
1410 Each `exec` can return a value combined with a type in `struct lrval`.
1411 The type may be `Tnone` but must be non-NULL. Some `exec`s will return
1412 the location of a value, which can be updated, in `lval`. Others will
1413 set `lval` to NULL indicating that there is a value of appropriate type
1417 ###### core functions
1421 struct value rval, *lval;
1424 static struct lrval _interp_exec(struct exec *e);
1426 static struct value interp_exec(struct exec *e, struct type **typeret)
1428 struct lrval ret = _interp_exec(e);
1430 if (!ret.type) abort();
1432 *typeret = ret.type;
1434 dup_value(ret.type, ret.lval, &ret.rval);
1438 static struct value *linterp_exec(struct exec *e, struct type **typeret)
1440 struct lrval ret = _interp_exec(e);
1443 *typeret = ret.type;
1445 free_value(ret.type, &ret.rval);
1449 static struct lrval _interp_exec(struct exec *e)
1452 struct value rv = {}, *lrv = NULL;
1453 struct type *rvtype;
1455 rvtype = ret.type = Tnone;
1465 struct binode *b = cast(binode, e);
1466 struct value left, right, *lleft;
1467 struct type *ltype, *rtype;
1468 ltype = rtype = Tnone;
1470 ## interp binode cases
1472 free_value(ltype, &left);
1473 free_value(rtype, &right);
1476 ## interp exec cases
1486 Now that we have the shape of the interpreter in place we can add some
1487 complex types and connected them in to the data structures and the
1488 different phases of parse, analyse, print, interpret.
1490 Thus far we have arrays and structs.
1494 Arrays can be declared by giving a size and a type, as `[size]type' so
1495 `freq:[26]number` declares `freq` to be an array of 26 numbers. The
1496 size can be either a literal number, or a named constant. Some day an
1497 arbitrary expression will be supported.
1499 Arrays cannot be assigned. When pointers are introduced we will also
1500 introduce array slices which can refer to part or all of an array -
1501 the assignment syntax will create a slice. For now, an array can only
1502 ever be referenced by the name it is declared with. It is likely that
1503 a "`copy`" primitive will eventually be define which can be used to
1504 make a copy of an array with controllable recursive depth.
1506 ###### type union fields
1510 struct variable *vsize;
1511 struct type *member;
1514 ###### value functions
1516 static void array_prepare_type(struct type *type)
1519 if (!type->array.vsize)
1523 mpz_tdiv_q(q, mpq_numref(type->array.vsize->val->num),
1524 mpq_denref(type->array.vsize->val->num));
1525 type->array.size = mpz_get_si(q);
1528 type->size = type->array.size * type->array.member->size;
1529 type->align = type->array.member->align;
1532 static void array_init(struct type *type, struct value *val)
1538 for (i = 0; i < type->array.size; i++) {
1540 v = (void*)val->ptr + i * type->array.member->size;
1541 val_init(type->array.member, v);
1545 static void array_free(struct type *type, struct value *val)
1549 for (i = 0; i < type->array.size; i++) {
1551 v = (void*)val->ptr + i * type->array.member->size;
1552 free_value(type->array.member, v);
1556 static int array_compat(struct type *require, struct type *have)
1558 if (have->compat != require->compat)
1560 /* Both are arrays, so we can look at details */
1561 if (!type_compat(require->array.member, have->array.member, 0))
1563 if (require->array.vsize == NULL && have->array.vsize == NULL)
1564 return require->array.size == have->array.size;
1566 return require->array.vsize == have->array.vsize;
1569 static void array_print_type(struct type *type, FILE *f)
1572 if (type->array.vsize) {
1573 struct binding *b = type->array.vsize->name;
1574 fprintf(f, "%.*s]", b->name.len, b->name.txt);
1576 fprintf(f, "%d]", type->array.size);
1577 type_print(type->array.member, f);
1580 static struct type array_prototype = {
1582 .prepare_type = array_prepare_type,
1583 .print_type = array_print_type,
1584 .compat = array_compat,
1588 ###### declare terminals
1593 | [ NUMBER ] Type ${ {
1596 struct text noname = { "", 0 };
1599 $0 = t = add_type(c, noname, &array_prototype);
1600 t->array.member = $<4;
1601 t->array.vsize = NULL;
1602 if (number_parse(num, tail, $2.txt) == 0)
1603 tok_err(c, "error: unrecognised number", &$2);
1605 tok_err(c, "error: unsupported number suffix", &$2);
1607 t->array.size = mpz_get_ui(mpq_numref(num));
1608 if (mpz_cmp_ui(mpq_denref(num), 1) != 0) {
1609 tok_err(c, "error: array size must be an integer",
1611 } else if (mpz_cmp_ui(mpq_numref(num), 1UL << 30) >= 0)
1612 tok_err(c, "error: array size is too large",
1616 t->size = t->array.size * t->array.member->size;
1617 t->align = t->array.member->align;
1620 | [ IDENTIFIER ] Type ${ {
1621 struct variable *v = var_ref(c, $2.txt);
1622 struct text noname = { "", 0 };
1625 tok_err(c, "error: name undeclared", &$2);
1626 else if (!v->constant)
1627 tok_err(c, "error: array size must be a constant", &$2);
1629 $0 = add_type(c, noname, &array_prototype);
1630 $0->array.member = $<4;
1632 $0->array.vsize = v;
1638 ###### variable grammar
1640 | Variable [ Expression ] ${ {
1641 struct binode *b = new(binode);
1648 ###### print binode cases
1650 print_exec(b->left, -1, bracket);
1652 print_exec(b->right, -1, bracket);
1656 ###### propagate binode cases
1658 /* left must be an array, right must be a number,
1659 * result is the member type of the array
1661 propagate_types(b->right, c, ok, Tnum, 0);
1662 t = propagate_types(b->left, c, ok, NULL, rules & Rnoconstant);
1663 if (!t || t->compat != array_compat) {
1664 type_err(c, "error: %1 cannot be indexed", prog, t, 0, NULL);
1667 if (!type_compat(type, t->array.member, rules)) {
1668 type_err(c, "error: have %1 but need %2", prog,
1669 t->array.member, rules, type);
1671 return t->array.member;
1675 ###### interp binode cases
1680 lleft = linterp_exec(b->left, <ype);
1681 right = interp_exec(b->right, &rtype);
1683 mpz_tdiv_q(q, mpq_numref(right.num), mpq_denref(right.num));
1687 rvtype = ltype->array.member;
1688 if (i >= 0 && i < ltype->array.size)
1689 lrv = (void*)lleft + i * rvtype->size;
1691 val_init(ltype->array.member, &rv);
1698 A `struct` is a data-type that contains one or more other data-types.
1699 It differs from an array in that each member can be of a different
1700 type, and they are accessed by name rather than by number. Thus you
1701 cannot choose an element by calculation, you need to know what you
1704 The language makes no promises about how a given structure will be
1705 stored in memory - it is free to rearrange fields to suit whatever
1706 criteria seems important.
1708 Structs are declared separately from program code - they cannot be
1709 declared in-line in a variable declaration like arrays can. A struct
1710 is given a name and this name is used to identify the type - the name
1711 is not prefixed by the word `struct` as it would be in C.
1713 Structs are only treated as the same if they have the same name.
1714 Simply having the same fields in the same order is not enough. This
1715 might change once we can create structure initializers from a list of
1718 Each component datum is identified much like a variable is declared,
1719 with a name, one or two colons, and a type. The type cannot be omitted
1720 as there is no opportunity to deduce the type from usage. An initial
1721 value can be given following an equals sign, so
1723 ##### Example: a struct type
1729 would declare a type called "complex" which has two number fields,
1730 each initialised to zero.
1732 Struct will need to be declared separately from the code that uses
1733 them, so we will need to be able to print out the declaration of a
1734 struct when reprinting the whole program. So a `print_type_decl` type
1735 function will be needed.
1737 ###### type union fields
1749 ###### type functions
1750 void (*print_type_decl)(struct type *type, FILE *f);
1752 ###### value functions
1754 static void structure_init(struct type *type, struct value *val)
1758 for (i = 0; i < type->structure.nfields; i++) {
1760 v = (void*) val->ptr + type->structure.fields[i].offset;
1761 val_init(type->structure.fields[i].type, v);
1765 static void structure_free(struct type *type, struct value *val)
1769 for (i = 0; i < type->structure.nfields; i++) {
1771 v = (void*)val->ptr + type->structure.fields[i].offset;
1772 free_value(type->structure.fields[i].type, v);
1776 static void structure_free_type(struct type *t)
1779 for (i = 0; i < t->structure.nfields; i++)
1780 if (t->structure.fields[i].init) {
1781 free_value(t->structure.fields[i].type,
1782 t->structure.fields[i].init);
1783 free(t->structure.fields[i].init);
1785 free(t->structure.fields);
1788 static struct type structure_prototype = {
1789 .init = structure_init,
1790 .free = structure_free,
1791 .free_type = structure_free_type,
1792 .print_type_decl = structure_print_type,
1806 ###### free exec cases
1808 free_exec(cast(fieldref, e)->left);
1812 ###### declare terminals
1815 ###### variable grammar
1817 | Variable . IDENTIFIER ${ {
1818 struct fieldref *fr = new_pos(fieldref, $2);
1825 ###### print exec cases
1829 struct fieldref *f = cast(fieldref, e);
1830 print_exec(f->left, -1, bracket);
1831 printf(".%.*s", f->name.len, f->name.txt);
1835 ###### ast functions
1836 static int find_struct_index(struct type *type, struct text field)
1839 for (i = 0; i < type->structure.nfields; i++)
1840 if (text_cmp(type->structure.fields[i].name, field) == 0)
1845 ###### propagate exec cases
1849 struct fieldref *f = cast(fieldref, prog);
1850 struct type *st = propagate_types(f->left, c, ok, NULL, 0);
1853 type_err(c, "error: unknown type for field access", f->left,
1855 else if (st->init != structure_init)
1856 type_err(c, "error: field reference attempted on %1, not a struct",
1857 f->left, st, 0, NULL);
1858 else if (f->index == -2) {
1859 f->index = find_struct_index(st, f->name);
1861 type_err(c, "error: cannot find requested field in %1",
1862 f->left, st, 0, NULL);
1864 if (f->index >= 0) {
1865 struct type *ft = st->structure.fields[f->index].type;
1866 if (!type_compat(type, ft, rules))
1867 type_err(c, "error: have %1 but need %2", prog,
1874 ###### interp exec cases
1877 struct fieldref *f = cast(fieldref, e);
1879 struct value *lleft = linterp_exec(f->left, <ype);
1880 lrv = (void*)lleft->ptr + ltype->structure.fields[f->index].offset;
1881 rvtype = ltype->structure.fields[f->index].type;
1887 struct fieldlist *prev;
1891 ###### ast functions
1892 static void free_fieldlist(struct fieldlist *f)
1896 free_fieldlist(f->prev);
1898 free_value(f->f.type, f->f.init);
1904 ###### top level grammar
1905 DeclareStruct -> struct IDENTIFIER FieldBlock Newlines ${ {
1907 add_type(c, $2.txt, &structure_prototype);
1909 struct fieldlist *f;
1911 for (f = $3; f; f=f->prev)
1914 t->structure.nfields = cnt;
1915 t->structure.fields = calloc(cnt, sizeof(struct field));
1918 int a = f->f.type->align;
1920 t->structure.fields[cnt] = f->f;
1921 if (t->size & (a-1))
1922 t->size = (t->size | (a-1)) + 1;
1923 t->structure.fields[cnt].offset = t->size;
1924 t->size += ((f->f.type->size - 1) | (a-1)) + 1;
1933 FieldBlock -> { IN OptNL FieldLines OUT OptNL } ${ $0 = $<FL; }$
1934 | { SimpleFieldList } ${ $0 = $<SFL; }$
1935 | IN OptNL FieldLines OUT ${ $0 = $<FL; }$
1936 | SimpleFieldList EOL ${ $0 = $<SFL; }$
1938 FieldLines -> SimpleFieldList Newlines ${ $0 = $<SFL; }$
1939 | FieldLines SimpleFieldList Newlines ${
1944 SimpleFieldList -> Field ${ $0 = $<F; }$
1945 | SimpleFieldList ; Field ${
1949 | SimpleFieldList ; ${
1952 | ERROR ${ tok_err(c, "Syntax error in struct field", &$1); }$
1954 Field -> IDENTIFIER : Type = Expression ${ {
1957 $0 = calloc(1, sizeof(struct fieldlist));
1958 $0->f.name = $1.txt;
1963 propagate_types($<5, c, &ok, $3, 0);
1968 struct value vl = interp_exec($5, NULL);
1969 $0->f.init = val_alloc($0->f.type, &vl);
1972 | IDENTIFIER : Type ${
1973 $0 = calloc(1, sizeof(struct fieldlist));
1974 $0->f.name = $1.txt;
1976 $0->f.init = val_alloc($0->f.type, NULL);
1979 ###### forward decls
1980 static void structure_print_type(struct type *t, FILE *f);
1982 ###### value functions
1983 static void structure_print_type(struct type *t, FILE *f)
1987 fprintf(f, "struct %.*s\n", t->name.len, t->name.txt);
1989 for (i = 0; i < t->structure.nfields; i++) {
1990 struct field *fl = t->structure.fields + i;
1991 fprintf(f, " %.*s : ", fl->name.len, fl->name.txt);
1992 type_print(fl->type, f);
1993 if (fl->type->print && fl->init) {
1995 if (fl->type == Tstr)
1997 print_value(fl->type, fl->init);
1998 if (fl->type == Tstr)
2005 ###### print type decls
2010 while (target != 0) {
2012 for (t = context.typelist; t ; t=t->next)
2013 if (t->print_type_decl) {
2022 t->print_type_decl(t, stdout);
2028 ## Executables: the elements of code
2030 Each code element needs to be parsed, printed, analysed,
2031 interpreted, and freed. There are several, so let's just start with
2032 the easy ones and work our way up.
2036 We have already met values as separate objects. When manifest
2037 constants appear in the program text, that must result in an executable
2038 which has a constant value. So the `val` structure embeds a value in
2051 ###### ast functions
2052 struct val *new_val(struct type *T, struct token tk)
2054 struct val *v = new_pos(val, tk);
2065 $0 = new_val(Tbool, $1);
2069 $0 = new_val(Tbool, $1);
2073 $0 = new_val(Tnum, $1);
2076 if (number_parse($0->val.num, tail, $1.txt) == 0)
2077 mpq_init($0->val.num);
2079 tok_err(c, "error: unsupported number suffix",
2084 $0 = new_val(Tstr, $1);
2087 string_parse(&$1, '\\', &$0->val.str, tail);
2089 tok_err(c, "error: unsupported string suffix",
2094 $0 = new_val(Tstr, $1);
2097 string_parse(&$1, '\\', &$0->val.str, tail);
2099 tok_err(c, "error: unsupported string suffix",
2104 ###### print exec cases
2107 struct val *v = cast(val, e);
2108 if (v->vtype == Tstr)
2110 print_value(v->vtype, &v->val);
2111 if (v->vtype == Tstr)
2116 ###### propagate exec cases
2119 struct val *val = cast(val, prog);
2120 if (!type_compat(type, val->vtype, rules))
2121 type_err(c, "error: expected %1%r found %2",
2122 prog, type, rules, val->vtype);
2126 ###### interp exec cases
2128 rvtype = cast(val, e)->vtype;
2129 dup_value(rvtype, &cast(val, e)->val, &rv);
2132 ###### ast functions
2133 static void free_val(struct val *v)
2136 free_value(v->vtype, &v->val);
2140 ###### free exec cases
2141 case Xval: free_val(cast(val, e)); break;
2143 ###### ast functions
2144 // Move all nodes from 'b' to 'rv', reversing their order.
2145 // In 'b' 'left' is a list, and 'right' is the last node.
2146 // In 'rv', left' is the first node and 'right' is a list.
2147 static struct binode *reorder_bilist(struct binode *b)
2149 struct binode *rv = NULL;
2152 struct exec *t = b->right;
2156 b = cast(binode, b->left);
2166 Just as we used a `val` to wrap a value into an `exec`, we similarly
2167 need a `var` to wrap a `variable` into an exec. While each `val`
2168 contained a copy of the value, each `var` holds a link to the variable
2169 because it really is the same variable no matter where it appears.
2170 When a variable is used, we need to remember to follow the `->merged`
2171 link to find the primary instance.
2179 struct variable *var;
2187 VariableDecl -> IDENTIFIER : ${ {
2188 struct variable *v = var_decl(c, $1.txt);
2189 $0 = new_pos(var, $1);
2194 v = var_ref(c, $1.txt);
2196 type_err(c, "error: variable '%v' redeclared",
2198 type_err(c, "info: this is where '%v' was first declared",
2199 v->where_decl, NULL, 0, NULL);
2202 | IDENTIFIER :: ${ {
2203 struct variable *v = var_decl(c, $1.txt);
2204 $0 = new_pos(var, $1);
2210 v = var_ref(c, $1.txt);
2212 type_err(c, "error: variable '%v' redeclared",
2214 type_err(c, "info: this is where '%v' was first declared",
2215 v->where_decl, NULL, 0, NULL);
2218 | IDENTIFIER : Type ${ {
2219 struct variable *v = var_decl(c, $1.txt);
2220 $0 = new_pos(var, $1);
2228 v = var_ref(c, $1.txt);
2230 type_err(c, "error: variable '%v' redeclared",
2232 type_err(c, "info: this is where '%v' was first declared",
2233 v->where_decl, NULL, 0, NULL);
2236 | IDENTIFIER :: Type ${ {
2237 struct variable *v = var_decl(c, $1.txt);
2238 $0 = new_pos(var, $1);
2247 v = var_ref(c, $1.txt);
2249 type_err(c, "error: variable '%v' redeclared",
2251 type_err(c, "info: this is where '%v' was first declared",
2252 v->where_decl, NULL, 0, NULL);
2257 Variable -> IDENTIFIER ${ {
2258 struct variable *v = var_ref(c, $1.txt);
2259 $0 = new_pos(var, $1);
2261 /* This might be a label - allocate a var just in case */
2262 v = var_decl(c, $1.txt);
2270 cast(var, $0)->var = v;
2275 Type -> IDENTIFIER ${
2276 $0 = find_type(c, $1.txt);
2279 "error: undefined type", &$1);
2286 ###### print exec cases
2289 struct var *v = cast(var, e);
2291 struct binding *b = v->var->name;
2292 printf("%.*s", b->name.len, b->name.txt);
2299 if (loc->type == Xvar) {
2300 struct var *v = cast(var, loc);
2302 struct binding *b = v->var->name;
2303 fprintf(stderr, "%.*s", b->name.len, b->name.txt);
2305 fputs("???", stderr); // NOTEST
2307 fputs("NOTVAR", stderr); // NOTEST
2310 ###### propagate exec cases
2314 struct var *var = cast(var, prog);
2315 struct variable *v = var->var;
2317 type_err(c, "%d:BUG: no variable!!", prog, NULL, 0, NULL); // NOTEST
2318 return Tnone; // NOTEST
2322 if (v->constant && (rules & Rnoconstant)) {
2323 type_err(c, "error: Cannot assign to a constant: %v",
2324 prog, NULL, 0, NULL);
2325 type_err(c, "info: name was defined as a constant here",
2326 v->where_decl, NULL, 0, NULL);
2329 if (v->type == Tnone && v->where_decl == prog)
2330 type_err(c, "error: variable used but not declared: %v",
2331 prog, NULL, 0, NULL);
2332 if (v->type == NULL) {
2333 if (type && *ok != 0) {
2336 v->where_set = prog;
2341 if (!type_compat(type, v->type, rules)) {
2342 type_err(c, "error: expected %1%r but variable '%v' is %2", prog,
2343 type, rules, v->type);
2344 type_err(c, "info: this is where '%v' was set to %1", v->where_set,
2345 v->type, rules, NULL);
2352 ###### interp exec cases
2355 struct var *var = cast(var, e);
2356 struct variable *v = var->var;
2365 ###### ast functions
2367 static void free_var(struct var *v)
2372 ###### free exec cases
2373 case Xvar: free_var(cast(var, e)); break;
2375 ### Expressions: Conditional
2377 Our first user of the `binode` will be conditional expressions, which
2378 is a bit odd as they actually have three components. That will be
2379 handled by having 2 binodes for each expression. The conditional
2380 expression is the lowest precedence operator which is why we define it
2381 first - to start the precedence list.
2383 Conditional expressions are of the form "value `if` condition `else`
2384 other_value". They associate to the right, so everything to the right
2385 of `else` is part of an else value, while only a higher-precedence to
2386 the left of `if` is the if values. Between `if` and `else` there is no
2387 room for ambiguity, so a full conditional expression is allowed in
2399 Expression -> Expression if Expression else Expression $$ifelse ${ {
2400 struct binode *b1 = new(binode);
2401 struct binode *b2 = new(binode);
2410 ## expression grammar
2412 ###### print binode cases
2415 b2 = cast(binode, b->right);
2416 if (bracket) printf("(");
2417 print_exec(b2->left, -1, bracket);
2419 print_exec(b->left, -1, bracket);
2421 print_exec(b2->right, -1, bracket);
2422 if (bracket) printf(")");
2425 ###### propagate binode cases
2428 /* cond must be Tbool, others must match */
2429 struct binode *b2 = cast(binode, b->right);
2432 propagate_types(b->left, c, ok, Tbool, 0);
2433 t = propagate_types(b2->left, c, ok, type, Rnolabel);
2434 t2 = propagate_types(b2->right, c, ok, type ?: t, Rnolabel);
2438 ###### interp binode cases
2441 struct binode *b2 = cast(binode, b->right);
2442 left = interp_exec(b->left, <ype);
2444 rv = interp_exec(b2->left, &rvtype);
2446 rv = interp_exec(b2->right, &rvtype);
2450 ### Expressions: Boolean
2452 The next class of expressions to use the `binode` will be Boolean
2453 expressions. "`and then`" and "`or else`" are similar to `and` and `or`
2454 have same corresponding precendence. The difference is that they don't
2455 evaluate the second expression if not necessary.
2464 ###### expr precedence
2469 ###### expression grammar
2470 | Expression or Expression ${ {
2471 struct binode *b = new(binode);
2477 | Expression or else Expression ${ {
2478 struct binode *b = new(binode);
2485 | Expression and Expression ${ {
2486 struct binode *b = new(binode);
2492 | Expression and then Expression ${ {
2493 struct binode *b = new(binode);
2500 | not Expression ${ {
2501 struct binode *b = new(binode);
2507 ###### print binode cases
2509 if (bracket) printf("(");
2510 print_exec(b->left, -1, bracket);
2512 print_exec(b->right, -1, bracket);
2513 if (bracket) printf(")");
2516 if (bracket) printf("(");
2517 print_exec(b->left, -1, bracket);
2518 printf(" and then ");
2519 print_exec(b->right, -1, bracket);
2520 if (bracket) printf(")");
2523 if (bracket) printf("(");
2524 print_exec(b->left, -1, bracket);
2526 print_exec(b->right, -1, bracket);
2527 if (bracket) printf(")");
2530 if (bracket) printf("(");
2531 print_exec(b->left, -1, bracket);
2532 printf(" or else ");
2533 print_exec(b->right, -1, bracket);
2534 if (bracket) printf(")");
2537 if (bracket) printf("(");
2539 print_exec(b->right, -1, bracket);
2540 if (bracket) printf(")");
2543 ###### propagate binode cases
2549 /* both must be Tbool, result is Tbool */
2550 propagate_types(b->left, c, ok, Tbool, 0);
2551 propagate_types(b->right, c, ok, Tbool, 0);
2552 if (type && type != Tbool)
2553 type_err(c, "error: %1 operation found where %2 expected", prog,
2557 ###### interp binode cases
2559 rv = interp_exec(b->left, &rvtype);
2560 right = interp_exec(b->right, &rtype);
2561 rv.bool = rv.bool && right.bool;
2564 rv = interp_exec(b->left, &rvtype);
2566 rv = interp_exec(b->right, NULL);
2569 rv = interp_exec(b->left, &rvtype);
2570 right = interp_exec(b->right, &rtype);
2571 rv.bool = rv.bool || right.bool;
2574 rv = interp_exec(b->left, &rvtype);
2576 rv = interp_exec(b->right, NULL);
2579 rv = interp_exec(b->right, &rvtype);
2583 ### Expressions: Comparison
2585 Of slightly higher precedence that Boolean expressions are Comparisons.
2586 A comparison takes arguments of any comparable type, but the two types
2589 To simplify the parsing we introduce an `eop` which can record an
2590 expression operator, and the `CMPop` non-terminal will match one of them.
2597 ###### ast functions
2598 static void free_eop(struct eop *e)
2612 ###### expr precedence
2613 $LEFT < > <= >= == != CMPop
2615 ###### expression grammar
2616 | Expression CMPop Expression ${ {
2617 struct binode *b = new(binode);
2627 CMPop -> < ${ $0.op = Less; }$
2628 | > ${ $0.op = Gtr; }$
2629 | <= ${ $0.op = LessEq; }$
2630 | >= ${ $0.op = GtrEq; }$
2631 | == ${ $0.op = Eql; }$
2632 | != ${ $0.op = NEql; }$
2634 ###### print binode cases
2642 if (bracket) printf("(");
2643 print_exec(b->left, -1, bracket);
2645 case Less: printf(" < "); break;
2646 case LessEq: printf(" <= "); break;
2647 case Gtr: printf(" > "); break;
2648 case GtrEq: printf(" >= "); break;
2649 case Eql: printf(" == "); break;
2650 case NEql: printf(" != "); break;
2651 default: abort(); // NOTEST
2653 print_exec(b->right, -1, bracket);
2654 if (bracket) printf(")");
2657 ###### propagate binode cases
2664 /* Both must match but not be labels, result is Tbool */
2665 t = propagate_types(b->left, c, ok, NULL, Rnolabel);
2667 propagate_types(b->right, c, ok, t, 0);
2669 t = propagate_types(b->right, c, ok, NULL, Rnolabel);
2671 t = propagate_types(b->left, c, ok, t, 0);
2673 if (!type_compat(type, Tbool, 0))
2674 type_err(c, "error: Comparison returns %1 but %2 expected", prog,
2675 Tbool, rules, type);
2678 ###### interp binode cases
2687 left = interp_exec(b->left, <ype);
2688 right = interp_exec(b->right, &rtype);
2689 cmp = value_cmp(ltype, rtype, &left, &right);
2692 case Less: rv.bool = cmp < 0; break;
2693 case LessEq: rv.bool = cmp <= 0; break;
2694 case Gtr: rv.bool = cmp > 0; break;
2695 case GtrEq: rv.bool = cmp >= 0; break;
2696 case Eql: rv.bool = cmp == 0; break;
2697 case NEql: rv.bool = cmp != 0; break;
2698 default: rv.bool = 0; break; // NOTEST
2703 ### Expressions: The rest
2705 The remaining expressions with the highest precedence are arithmetic,
2706 string concatenation, and string conversion. String concatenation
2707 (`++`) has the same precedence as multiplication and division, but lower
2710 String conversion is a temporary feature until I get a better type
2711 system. `$` is a prefix operator which expects a string and returns
2714 `+` and `-` are both infix and prefix operations (where they are
2715 absolute value and negation). These have different operator names.
2717 We also have a 'Bracket' operator which records where parentheses were
2718 found. This makes it easy to reproduce these when printing. Possibly I
2719 should only insert brackets were needed for precedence.
2729 ###### expr precedence
2735 ###### expression grammar
2736 | Expression Eop Expression ${ {
2737 struct binode *b = new(binode);
2744 | Expression Top Expression ${ {
2745 struct binode *b = new(binode);
2752 | ( Expression ) ${ {
2753 struct binode *b = new_pos(binode, $1);
2758 | Uop Expression ${ {
2759 struct binode *b = new(binode);
2764 | Value ${ $0 = $<1; }$
2765 | Variable ${ $0 = $<1; }$
2768 Eop -> + ${ $0.op = Plus; }$
2769 | - ${ $0.op = Minus; }$
2771 Uop -> + ${ $0.op = Absolute; }$
2772 | - ${ $0.op = Negate; }$
2773 | $ ${ $0.op = StringConv; }$
2775 Top -> * ${ $0.op = Times; }$
2776 | / ${ $0.op = Divide; }$
2777 | % ${ $0.op = Rem; }$
2778 | ++ ${ $0.op = Concat; }$
2780 ###### print binode cases
2787 if (bracket) printf("(");
2788 print_exec(b->left, indent, bracket);
2790 case Plus: fputs(" + ", stdout); break;
2791 case Minus: fputs(" - ", stdout); break;
2792 case Times: fputs(" * ", stdout); break;
2793 case Divide: fputs(" / ", stdout); break;
2794 case Rem: fputs(" % ", stdout); break;
2795 case Concat: fputs(" ++ ", stdout); break;
2796 default: abort(); // NOTEST
2798 print_exec(b->right, indent, bracket);
2799 if (bracket) printf(")");
2804 if (bracket) printf("(");
2806 case Absolute: fputs("+", stdout); break;
2807 case Negate: fputs("-", stdout); break;
2808 case StringConv: fputs("$", stdout); break;
2809 default: abort(); // NOTEST
2811 print_exec(b->right, indent, bracket);
2812 if (bracket) printf(")");
2816 print_exec(b->right, indent, bracket);
2820 ###### propagate binode cases
2826 /* both must be numbers, result is Tnum */
2829 /* as propagate_types ignores a NULL,
2830 * unary ops fit here too */
2831 propagate_types(b->left, c, ok, Tnum, 0);
2832 propagate_types(b->right, c, ok, Tnum, 0);
2833 if (!type_compat(type, Tnum, 0))
2834 type_err(c, "error: Arithmetic returns %1 but %2 expected", prog,
2839 /* both must be Tstr, result is Tstr */
2840 propagate_types(b->left, c, ok, Tstr, 0);
2841 propagate_types(b->right, c, ok, Tstr, 0);
2842 if (!type_compat(type, Tstr, 0))
2843 type_err(c, "error: Concat returns %1 but %2 expected", prog,
2848 /* op must be string, result is number */
2849 propagate_types(b->left, c, ok, Tstr, 0);
2850 if (!type_compat(type, Tnum, 0))
2852 "error: Can only convert string to number, not %1",
2853 prog, type, 0, NULL);
2857 return propagate_types(b->right, c, ok, type, 0);
2859 ###### interp binode cases
2862 rv = interp_exec(b->left, &rvtype);
2863 right = interp_exec(b->right, &rtype);
2864 mpq_add(rv.num, rv.num, right.num);
2867 rv = interp_exec(b->left, &rvtype);
2868 right = interp_exec(b->right, &rtype);
2869 mpq_sub(rv.num, rv.num, right.num);
2872 rv = interp_exec(b->left, &rvtype);
2873 right = interp_exec(b->right, &rtype);
2874 mpq_mul(rv.num, rv.num, right.num);
2877 rv = interp_exec(b->left, &rvtype);
2878 right = interp_exec(b->right, &rtype);
2879 mpq_div(rv.num, rv.num, right.num);
2884 left = interp_exec(b->left, <ype);
2885 right = interp_exec(b->right, &rtype);
2886 mpz_init(l); mpz_init(r); mpz_init(rem);
2887 mpz_tdiv_q(l, mpq_numref(left.num), mpq_denref(left.num));
2888 mpz_tdiv_q(r, mpq_numref(right.num), mpq_denref(right.num));
2889 mpz_tdiv_r(rem, l, r);
2890 val_init(Tnum, &rv);
2891 mpq_set_z(rv.num, rem);
2892 mpz_clear(r); mpz_clear(l); mpz_clear(rem);
2897 rv = interp_exec(b->right, &rvtype);
2898 mpq_neg(rv.num, rv.num);
2901 rv = interp_exec(b->right, &rvtype);
2902 mpq_abs(rv.num, rv.num);
2905 rv = interp_exec(b->right, &rvtype);
2908 left = interp_exec(b->left, <ype);
2909 right = interp_exec(b->right, &rtype);
2911 rv.str = text_join(left.str, right.str);
2914 right = interp_exec(b->right, &rvtype);
2918 struct text tx = right.str;
2921 if (tx.txt[0] == '-') {
2926 if (number_parse(rv.num, tail, tx) == 0)
2929 mpq_neg(rv.num, rv.num);
2931 printf("Unsupported suffix: %.*s\n", tx.len, tx.txt);
2935 ###### value functions
2937 static struct text text_join(struct text a, struct text b)
2940 rv.len = a.len + b.len;
2941 rv.txt = malloc(rv.len);
2942 memcpy(rv.txt, a.txt, a.len);
2943 memcpy(rv.txt+a.len, b.txt, b.len);
2947 ### Blocks, Statements, and Statement lists.
2949 Now that we have expressions out of the way we need to turn to
2950 statements. There are simple statements and more complex statements.
2951 Simple statements do not contain (syntactic) newlines, complex statements do.
2953 Statements often come in sequences and we have corresponding simple
2954 statement lists and complex statement lists.
2955 The former comprise only simple statements separated by semicolons.
2956 The later comprise complex statements and simple statement lists. They are
2957 separated by newlines. Thus the semicolon is only used to separate
2958 simple statements on the one line. This may be overly restrictive,
2959 but I'm not sure I ever want a complex statement to share a line with
2962 Note that a simple statement list can still use multiple lines if
2963 subsequent lines are indented, so
2965 ###### Example: wrapped simple statement list
2970 is a single simple statement list. This might allow room for
2971 confusion, so I'm not set on it yet.
2973 A simple statement list needs no extra syntax. A complex statement
2974 list has two syntactic forms. It can be enclosed in braces (much like
2975 C blocks), or it can be introduced by an indent and continue until an
2976 unindented newline (much like Python blocks). With this extra syntax
2977 it is referred to as a block.
2979 Note that a block does not have to include any newlines if it only
2980 contains simple statements. So both of:
2982 if condition: a=b; d=f
2984 if condition { a=b; print f }
2988 In either case the list is constructed from a `binode` list with
2989 `Block` as the operator. When parsing the list it is most convenient
2990 to append to the end, so a list is a list and a statement. When using
2991 the list it is more convenient to consider a list to be a statement
2992 and a list. So we need a function to re-order a list.
2993 `reorder_bilist` serves this purpose.
2995 The only stand-alone statement we introduce at this stage is `pass`
2996 which does nothing and is represented as a `NULL` pointer in a `Block`
2997 list. Other stand-alone statements will follow once the infrastructure
3008 Block -> { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3009 | { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3010 | SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3011 | SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3012 | IN OptNL Statementlist OUT ${ $0 = $<Sl; }$
3014 OpenBlock -> OpenScope { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3015 | OpenScope { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3016 | OpenScope SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3017 | OpenScope SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3018 | IN OpenScope OptNL Statementlist OUT ${ $0 = $<Sl; }$
3020 UseBlock -> { OpenScope IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3021 | { OpenScope SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3022 | IN OpenScope OptNL Statementlist OUT ${ $0 = $<Sl; }$
3024 ColonBlock -> { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3025 | { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3026 | : SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3027 | : SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3028 | : IN OptNL Statementlist OUT ${ $0 = $<Sl; }$
3030 Statementlist -> ComplexStatements ${ $0 = reorder_bilist($<CS); }$
3032 ComplexStatements -> ComplexStatements ComplexStatement ${
3042 | ComplexStatement ${
3054 ComplexStatement -> SimpleStatements Newlines ${
3055 $0 = reorder_bilist($<SS);
3057 | SimpleStatements ; Newlines ${
3058 $0 = reorder_bilist($<SS);
3060 ## ComplexStatement Grammar
3063 SimpleStatements -> SimpleStatements ; SimpleStatement ${
3069 | SimpleStatement ${
3077 SimpleStatement -> pass ${ $0 = NULL; }$
3078 | ERROR ${ tok_err(c, "Syntax error in statement", &$1); }$
3079 ## SimpleStatement Grammar
3081 ###### print binode cases
3085 if (b->left == NULL)
3088 print_exec(b->left, indent, bracket);
3091 print_exec(b->right, indent, bracket);
3094 // block, one per line
3095 if (b->left == NULL)
3096 do_indent(indent, "pass\n");
3098 print_exec(b->left, indent, bracket);
3100 print_exec(b->right, indent, bracket);
3104 ###### propagate binode cases
3107 /* If any statement returns something other than Tnone
3108 * or Tbool then all such must return same type.
3109 * As each statement may be Tnone or something else,
3110 * we must always pass NULL (unknown) down, otherwise an incorrect
3111 * error might occur. We never return Tnone unless it is
3116 for (e = b; e; e = cast(binode, e->right)) {
3117 t = propagate_types(e->left, c, ok, NULL, rules);
3118 if ((rules & Rboolok) && t == Tbool)
3120 if (t && t != Tnone && t != Tbool) {
3124 type_err(c, "error: expected %1%r, found %2",
3125 e->left, type, rules, t);
3131 ###### interp binode cases
3133 while (rvtype == Tnone &&
3136 rv = interp_exec(b->left, &rvtype);
3137 b = cast(binode, b->right);
3141 ### The Print statement
3143 `print` is a simple statement that takes a comma-separated list of
3144 expressions and prints the values separated by spaces and terminated
3145 by a newline. No control of formatting is possible.
3147 `print` faces the same list-ordering issue as blocks, and uses the
3153 ##### expr precedence
3156 ###### SimpleStatement Grammar
3158 | print ExpressionList ${
3159 $0 = reorder_bilist($<2);
3161 | print ExpressionList , ${
3166 $0 = reorder_bilist($0);
3177 ExpressionList -> ExpressionList , Expression ${
3190 ###### print binode cases
3193 do_indent(indent, "print");
3197 print_exec(b->left, -1, bracket);
3201 b = cast(binode, b->right);
3207 ###### propagate binode cases
3210 /* don't care but all must be consistent */
3211 propagate_types(b->left, c, ok, NULL, Rnolabel);
3212 propagate_types(b->right, c, ok, NULL, Rnolabel);
3215 ###### interp binode cases
3221 for ( ; b; b = cast(binode, b->right))
3225 left = interp_exec(b->left, <ype);
3226 print_value(ltype, &left);
3227 free_value(ltype, &left);
3238 ###### Assignment statement
3240 An assignment will assign a value to a variable, providing it hasn't
3241 been declared as a constant. The analysis phase ensures that the type
3242 will be correct so the interpreter just needs to perform the
3243 calculation. There is a form of assignment which declares a new
3244 variable as well as assigning a value. If a name is assigned before
3245 it is declared, and error will be raised as the name is created as
3246 `Tlabel` and it is illegal to assign to such names.
3252 ###### declare terminals
3255 ###### SimpleStatement Grammar
3256 | Variable = Expression ${
3262 | VariableDecl = Expression ${
3270 if ($1->var->where_set == NULL) {
3272 "Variable declared with no type or value: %v",
3282 ###### print binode cases
3285 do_indent(indent, "");
3286 print_exec(b->left, indent, bracket);
3288 print_exec(b->right, indent, bracket);
3295 struct variable *v = cast(var, b->left)->var;
3296 do_indent(indent, "");
3297 print_exec(b->left, indent, bracket);
3298 if (cast(var, b->left)->var->constant) {
3299 if (v->where_decl == v->where_set) {
3301 type_print(v->type, stdout);
3306 if (v->where_decl == v->where_set) {
3308 type_print(v->type, stdout);
3315 print_exec(b->right, indent, bracket);
3322 ###### propagate binode cases
3326 /* Both must match and not be labels,
3327 * Type must support 'dup',
3328 * For Assign, left must not be constant.
3331 t = propagate_types(b->left, c, ok, NULL,
3332 Rnolabel | (b->op == Assign ? Rnoconstant : 0));
3337 if (propagate_types(b->right, c, ok, t, 0) != t)
3338 if (b->left->type == Xvar)
3339 type_err(c, "info: variable '%v' was set as %1 here.",
3340 cast(var, b->left)->var->where_set, t, rules, NULL);
3342 t = propagate_types(b->right, c, ok, NULL, Rnolabel);
3344 propagate_types(b->left, c, ok, t,
3345 (b->op == Assign ? Rnoconstant : 0));
3347 if (t && t->dup == NULL)
3348 type_err(c, "error: cannot assign value of type %1", b, t, 0, NULL);
3353 ###### interp binode cases
3356 lleft = linterp_exec(b->left, <ype);
3357 right = interp_exec(b->right, &rtype);
3359 free_value(ltype, lleft);
3360 dup_value(ltype, &right, lleft);
3367 struct variable *v = cast(var, b->left)->var;
3370 free_value(v->type, v->val);
3373 right = interp_exec(b->right, &rtype);
3374 v->val = val_alloc(v->type, &right);
3377 v->val = val_alloc(v->type, NULL);
3382 ### The `use` statement
3384 The `use` statement is the last "simple" statement. It is needed when
3385 the condition in a conditional statement is a block. `use` works much
3386 like `return` in C, but only completes the `condition`, not the whole
3392 ###### expr precedence
3395 ###### SimpleStatement Grammar
3397 $0 = new_pos(binode, $1);
3400 if ($0->right->type == Xvar) {
3401 struct var *v = cast(var, $0->right);
3402 if (v->var->type == Tnone) {
3403 /* Convert this to a label */
3404 v->var->type = Tlabel;
3405 v->var->val = val_alloc(Tlabel, NULL);
3406 v->var->val->label = v->var->val;
3411 ###### print binode cases
3414 do_indent(indent, "use ");
3415 print_exec(b->right, -1, bracket);
3420 ###### propagate binode cases
3423 /* result matches value */
3424 return propagate_types(b->right, c, ok, type, 0);
3426 ###### interp binode cases
3429 rv = interp_exec(b->right, &rvtype);
3432 ### The Conditional Statement
3434 This is the biggy and currently the only complex statement. This
3435 subsumes `if`, `while`, `do/while`, `switch`, and some parts of `for`.
3436 It is comprised of a number of parts, all of which are optional though
3437 set combinations apply. Each part is (usually) a key word (`then` is
3438 sometimes optional) followed by either an expression or a code block,
3439 except the `casepart` which is a "key word and an expression" followed
3440 by a code block. The code-block option is valid for all parts and,
3441 where an expression is also allowed, the code block can use the `use`
3442 statement to report a value. If the code block does not report a value
3443 the effect is similar to reporting `True`.
3445 The `else` and `case` parts, as well as `then` when combined with
3446 `if`, can contain a `use` statement which will apply to some
3447 containing conditional statement. `for` parts, `do` parts and `then`
3448 parts used with `for` can never contain a `use`, except in some
3449 subordinate conditional statement.
3451 If there is a `forpart`, it is executed first, only once.
3452 If there is a `dopart`, then it is executed repeatedly providing
3453 always that the `condpart` or `cond`, if present, does not return a non-True
3454 value. `condpart` can fail to return any value if it simply executes
3455 to completion. This is treated the same as returning `True`.
3457 If there is a `thenpart` it will be executed whenever the `condpart`
3458 or `cond` returns True (or does not return any value), but this will happen
3459 *after* `dopart` (when present).
3461 If `elsepart` is present it will be executed at most once when the
3462 condition returns `False` or some value that isn't `True` and isn't
3463 matched by any `casepart`. If there are any `casepart`s, they will be
3464 executed when the condition returns a matching value.
3466 The particular sorts of values allowed in case parts has not yet been
3467 determined in the language design, so nothing is prohibited.
3469 The various blocks in this complex statement potentially provide scope
3470 for variables as described earlier. Each such block must include the
3471 "OpenScope" nonterminal before parsing the block, and must call
3472 `var_block_close()` when closing the block.
3474 The code following "`if`", "`switch`" and "`for`" does not get its own
3475 scope, but is in a scope covering the whole statement, so names
3476 declared there cannot be redeclared elsewhere. Similarly the
3477 condition following "`while`" is in a scope the covers the body
3478 ("`do`" part) of the loop, and which does not allow conditional scope
3479 extension. Code following "`then`" (both looping and non-looping),
3480 "`else`" and "`case`" each get their own local scope.
3482 The type requirements on the code block in a `whilepart` are quite
3483 unusal. It is allowed to return a value of some identifiable type, in
3484 which case the loop aborts and an appropriate `casepart` is run, or it
3485 can return a Boolean, in which case the loop either continues to the
3486 `dopart` (on `True`) or aborts and runs the `elsepart` (on `False`).
3487 This is different both from the `ifpart` code block which is expected to
3488 return a Boolean, or the `switchpart` code block which is expected to
3489 return the same type as the casepart values. The correct analysis of
3490 the type of the `whilepart` code block is the reason for the
3491 `Rboolok` flag which is passed to `propagate_types()`.
3493 The `cond_statement` cannot fit into a `binode` so a new `exec` is
3502 struct exec *action;
3503 struct casepart *next;
3505 struct cond_statement {
3507 struct exec *forpart, *condpart, *dopart, *thenpart, *elsepart;
3508 struct casepart *casepart;
3511 ###### ast functions
3513 static void free_casepart(struct casepart *cp)
3517 free_exec(cp->value);
3518 free_exec(cp->action);
3525 static void free_cond_statement(struct cond_statement *s)
3529 free_exec(s->forpart);
3530 free_exec(s->condpart);
3531 free_exec(s->dopart);
3532 free_exec(s->thenpart);
3533 free_exec(s->elsepart);
3534 free_casepart(s->casepart);
3538 ###### free exec cases
3539 case Xcond_statement: free_cond_statement(cast(cond_statement, e)); break;
3541 ###### ComplexStatement Grammar
3542 | CondStatement ${ $0 = $<1; }$
3544 ###### expr precedence
3545 $TERM for then while do
3552 // A CondStatement must end with EOL, as does CondSuffix and
3554 // ForPart, ThenPart, SwitchPart, CasePart are non-empty and
3555 // may or may not end with EOL
3556 // WhilePart and IfPart include an appropriate Suffix
3559 // Both ForPart and Whilepart open scopes, and CondSuffix only
3560 // closes one - so in the first branch here we have another to close.
3561 CondStatement -> ForPart OptNL ThenPart OptNL WhilePart CondSuffix ${
3564 $0->thenpart = $<TP;
3565 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3566 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3567 var_block_close(c, CloseSequential);
3569 | ForPart OptNL WhilePart CondSuffix ${
3572 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3573 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3574 var_block_close(c, CloseSequential);
3576 | WhilePart CondSuffix ${
3578 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3579 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3581 | SwitchPart OptNL CasePart CondSuffix ${
3583 $0->condpart = $<SP;
3584 $CP->next = $0->casepart;
3585 $0->casepart = $<CP;
3587 | SwitchPart : IN OptNL CasePart CondSuffix OUT Newlines ${
3589 $0->condpart = $<SP;
3590 $CP->next = $0->casepart;
3591 $0->casepart = $<CP;
3593 | IfPart IfSuffix ${
3595 $0->condpart = $IP.condpart; $IP.condpart = NULL;
3596 $0->thenpart = $IP.thenpart; $IP.thenpart = NULL;
3597 // This is where we close an "if" statement
3598 var_block_close(c, CloseSequential);
3601 CondSuffix -> IfSuffix ${
3603 // This is where we close scope of the whole
3604 // "for" or "while" statement
3605 var_block_close(c, CloseSequential);
3607 | Newlines CasePart CondSuffix ${
3609 $CP->next = $0->casepart;
3610 $0->casepart = $<CP;
3612 | CasePart CondSuffix ${
3614 $CP->next = $0->casepart;
3615 $0->casepart = $<CP;
3618 IfSuffix -> Newlines ${ $0 = new(cond_statement); }$
3619 | Newlines ElsePart ${ $0 = $<EP; }$
3620 | ElsePart ${$0 = $<EP; }$
3622 ElsePart -> else OpenBlock Newlines ${
3623 $0 = new(cond_statement);
3624 $0->elsepart = $<OB;
3625 var_block_close(c, CloseElse);
3627 | else OpenScope CondStatement ${
3628 $0 = new(cond_statement);
3629 $0->elsepart = $<CS;
3630 var_block_close(c, CloseElse);
3634 CasePart -> case Expression OpenScope ColonBlock ${
3635 $0 = calloc(1,sizeof(struct casepart));
3638 var_block_close(c, CloseParallel);
3642 // These scopes are closed in CondSuffix
3643 ForPart -> for OpenBlock ${
3647 ThenPart -> then OpenBlock ${
3649 var_block_close(c, CloseSequential);
3653 // This scope is closed in CondSuffix
3654 WhilePart -> while UseBlock OptNL do Block ${
3658 | while OpenScope Expression ColonBlock ${
3659 $0.condpart = $<Exp;
3663 IfPart -> if UseBlock OptNL then OpenBlock ClosePara ${
3667 | if OpenScope Expression OpenScope ColonBlock ClosePara ${
3671 | if OpenScope Expression OpenScope OptNL then Block ClosePara ${
3677 // This scope is closed in CondSuffix
3678 SwitchPart -> switch OpenScope Expression ${
3681 | switch UseBlock ${
3685 ###### print exec cases
3687 case Xcond_statement:
3689 struct cond_statement *cs = cast(cond_statement, e);
3690 struct casepart *cp;
3692 do_indent(indent, "for");
3693 if (bracket) printf(" {\n"); else printf("\n");
3694 print_exec(cs->forpart, indent+1, bracket);
3697 do_indent(indent, "} then {\n");
3699 do_indent(indent, "then\n");
3700 print_exec(cs->thenpart, indent+1, bracket);
3702 if (bracket) do_indent(indent, "}\n");
3706 if (cs->condpart && cs->condpart->type == Xbinode &&
3707 cast(binode, cs->condpart)->op == Block) {
3709 do_indent(indent, "while {\n");
3711 do_indent(indent, "while\n");
3712 print_exec(cs->condpart, indent+1, bracket);
3714 do_indent(indent, "} do {\n");
3716 do_indent(indent, "do\n");
3717 print_exec(cs->dopart, indent+1, bracket);
3719 do_indent(indent, "}\n");
3721 do_indent(indent, "while ");
3722 print_exec(cs->condpart, 0, bracket);
3727 print_exec(cs->dopart, indent+1, bracket);
3729 do_indent(indent, "}\n");
3734 do_indent(indent, "switch");
3736 do_indent(indent, "if");
3737 if (cs->condpart && cs->condpart->type == Xbinode &&
3738 cast(binode, cs->condpart)->op == Block) {
3743 print_exec(cs->condpart, indent+1, bracket);
3745 do_indent(indent, "}\n");
3747 do_indent(indent, "then:\n");
3748 print_exec(cs->thenpart, indent+1, bracket);
3752 print_exec(cs->condpart, 0, bracket);
3758 print_exec(cs->thenpart, indent+1, bracket);
3760 do_indent(indent, "}\n");
3765 for (cp = cs->casepart; cp; cp = cp->next) {
3766 do_indent(indent, "case ");
3767 print_exec(cp->value, -1, 0);
3772 print_exec(cp->action, indent+1, bracket);
3774 do_indent(indent, "}\n");
3777 do_indent(indent, "else");
3782 print_exec(cs->elsepart, indent+1, bracket);
3784 do_indent(indent, "}\n");
3789 ###### propagate exec cases
3790 case Xcond_statement:
3792 // forpart and dopart must return Tnone
3793 // thenpart must return Tnone if there is a dopart,
3794 // otherwise it is like elsepart.
3796 // be bool if there is no casepart
3797 // match casepart->values if there is a switchpart
3798 // either be bool or match casepart->value if there
3800 // elsepart and casepart->action must match the return type
3801 // expected of this statement.
3802 struct cond_statement *cs = cast(cond_statement, prog);
3803 struct casepart *cp;
3805 t = propagate_types(cs->forpart, c, ok, Tnone, 0);
3806 if (!type_compat(Tnone, t, 0))
3808 t = propagate_types(cs->dopart, c, ok, Tnone, 0);
3809 if (!type_compat(Tnone, t, 0))
3812 t = propagate_types(cs->thenpart, c, ok, Tnone, 0);
3813 if (!type_compat(Tnone, t, 0))
3816 if (cs->casepart == NULL)
3817 propagate_types(cs->condpart, c, ok, Tbool, 0);
3819 /* Condpart must match case values, with bool permitted */
3821 for (cp = cs->casepart;
3822 cp && !t; cp = cp->next)
3823 t = propagate_types(cp->value, c, ok, NULL, 0);
3824 if (!t && cs->condpart)
3825 t = propagate_types(cs->condpart, c, ok, NULL, Rboolok);
3826 // Now we have a type (I hope) push it down
3828 for (cp = cs->casepart; cp; cp = cp->next)
3829 propagate_types(cp->value, c, ok, t, 0);
3830 propagate_types(cs->condpart, c, ok, t, Rboolok);
3833 // (if)then, else, and case parts must return expected type.
3834 if (!cs->dopart && !type)
3835 type = propagate_types(cs->thenpart, c, ok, NULL, rules);
3837 type = propagate_types(cs->elsepart, c, ok, NULL, rules);
3838 for (cp = cs->casepart;
3841 type = propagate_types(cp->action, c, ok, NULL, rules);
3844 propagate_types(cs->thenpart, c, ok, type, rules);
3845 propagate_types(cs->elsepart, c, ok, type, rules);
3846 for (cp = cs->casepart; cp ; cp = cp->next)
3847 propagate_types(cp->action, c, ok, type, rules);
3853 ###### interp exec cases
3854 case Xcond_statement:
3856 struct value v, cnd;
3857 struct type *vtype, *cndtype;
3858 struct casepart *cp;
3859 struct cond_statement *c = cast(cond_statement, e);
3862 interp_exec(c->forpart, NULL);
3865 cnd = interp_exec(c->condpart, &cndtype);
3868 if (!(cndtype == Tnone ||
3869 (cndtype == Tbool && cnd.bool != 0)))
3871 // cnd is Tnone or Tbool, doesn't need to be freed
3873 interp_exec(c->dopart, NULL);
3876 rv = interp_exec(c->thenpart, &rvtype);
3877 if (rvtype != Tnone || !c->dopart)
3879 free_value(rvtype, &rv);
3882 } while (c->dopart);
3884 for (cp = c->casepart; cp; cp = cp->next) {
3885 v = interp_exec(cp->value, &vtype);
3886 if (value_cmp(cndtype, vtype, &v, &cnd) == 0) {
3887 free_value(vtype, &v);
3888 free_value(cndtype, &cnd);
3889 rv = interp_exec(cp->action, &rvtype);
3892 free_value(vtype, &v);
3894 free_value(cndtype, &cnd);
3896 rv = interp_exec(c->elsepart, &rvtype);
3903 ### Top level structure
3905 All the language elements so far can be used in various places. Now
3906 it is time to clarify what those places are.
3908 At the top level of a file there will be a number of declarations.
3909 Many of the things that can be declared haven't been described yet,
3910 such as functions, procedures, imports, and probably more.
3911 For now there are two sorts of things that can appear at the top
3912 level. They are predefined constants, `struct` types, and the main
3913 program. While the syntax will allow the main program to appear
3914 multiple times, that will trigger an error if it is actually attempted.
3916 The various declarations do not return anything. They store the
3917 various declarations in the parse context.
3919 ###### Parser: grammar
3922 Ocean -> OptNL DeclarationList
3924 ## declare terminals
3931 DeclarationList -> Declaration
3932 | DeclarationList Declaration
3934 Declaration -> ERROR Newlines ${
3936 "error: unhandled parse error", &$1);
3942 ## top level grammar
3944 ### The `const` section
3946 As well as being defined in with the code that uses them, constants
3947 can be declared at the top level. These have full-file scope, so they
3948 are always `InScope`. The value of a top level constant can be given
3949 as an expression, and this is evaluated immediately rather than in the
3950 later interpretation stage. Once we add functions to the language, we
3951 will need rules concern which, if any, can be used to define a top
3954 Constants are defined in a section that starts with the reserved word
3955 `const` and then has a block with a list of assignment statements.
3956 For syntactic consistency, these must use the double-colon syntax to
3957 make it clear that they are constants. Type can also be given: if
3958 not, the type will be determined during analysis, as with other
3961 As the types constants are inserted at the head of a list, printing
3962 them in the same order that they were read is not straight forward.
3963 We take a quadratic approach here and count the number of constants
3964 (variables of depth 0), then count down from there, each time
3965 searching through for the Nth constant for decreasing N.
3967 ###### top level grammar
3971 DeclareConstant -> const { IN OptNL ConstList OUT OptNL } Newlines
3972 | const { SimpleConstList } Newlines
3973 | const IN OptNL ConstList OUT Newlines
3974 | const SimpleConstList Newlines
3976 ConstList -> ConstList SimpleConstLine
3978 SimpleConstList -> SimpleConstList ; Const
3981 SimpleConstLine -> SimpleConstList Newlines
3982 | ERROR Newlines ${ tok_err(c, "Syntax error in constant", &$1); }$
3985 CType -> Type ${ $0 = $<1; }$
3988 Const -> IDENTIFIER :: CType = Expression ${ {
3992 v = var_decl(c, $1.txt);
3994 struct var *var = new_pos(var, $1);
3995 v->where_decl = var;
4000 v = var_ref(c, $1.txt);
4001 tok_err(c, "error: name already declared", &$1);
4002 type_err(c, "info: this is where '%v' was first declared",
4003 v->where_decl, NULL, 0, NULL);
4007 propagate_types($5, c, &ok, $3, 0);
4012 struct value res = interp_exec($5, &v->type);
4013 v->val = val_alloc(v->type, &res);
4017 ###### print const decls
4022 while (target != 0) {
4024 for (v = context.in_scope; v; v=v->in_scope)
4025 if (v->depth == 0) {
4036 printf(" %.*s :: ", v->name->name.len, v->name->name.txt);
4037 type_print(v->type, stdout);
4039 if (v->type == Tstr)
4041 print_value(v->type, v->val);
4042 if (v->type == Tstr)
4050 ### Finally the whole program.
4052 Somewhat reminiscent of Pascal a (current) Ocean program starts with
4053 the keyword "program" and a list of variable names which are assigned
4054 values from command line arguments. Following this is a `block` which
4055 is the code to execute. Unlike Pascal, constants and other
4056 declarations come *before* the program.
4058 As this is the top level, several things are handled a bit
4060 The whole program is not interpreted by `interp_exec` as that isn't
4061 passed the argument list which the program requires. Similarly type
4062 analysis is a bit more interesting at this level.
4067 ###### top level grammar
4069 DeclareProgram -> Program ${ {
4071 type_err(c, "Program defined a second time",
4080 Program -> program OpenScope Varlist ColonBlock Newlines ${
4083 $0->left = reorder_bilist($<Vl);
4085 var_block_close(c, CloseSequential);
4086 if (c->scope_stack && !c->parse_error) abort();
4089 Varlist -> Varlist ArgDecl ${
4098 ArgDecl -> IDENTIFIER ${ {
4099 struct variable *v = var_decl(c, $1.txt);
4106 ###### print binode cases
4108 do_indent(indent, "program");
4109 for (b2 = cast(binode, b->left); b2; b2 = cast(binode, b2->right)) {
4111 print_exec(b2->left, 0, 0);
4117 print_exec(b->right, indent+1, bracket);
4119 do_indent(indent, "}\n");
4122 ###### propagate binode cases
4123 case Program: abort(); // NOTEST
4125 ###### core functions
4127 static int analyse_prog(struct exec *prog, struct parse_context *c)
4129 struct binode *b = cast(binode, prog);
4136 propagate_types(b->right, c, &ok, Tnone, 0);
4141 for (b = cast(binode, b->left); b; b = cast(binode, b->right)) {
4142 struct var *v = cast(var, b->left);
4143 if (!v->var->type) {
4144 v->var->where_set = b;
4145 v->var->type = Tstr;
4149 b = cast(binode, prog);
4152 propagate_types(b->right, c, &ok, Tnone, 0);
4157 /* Make sure everything is still consistent */
4158 propagate_types(b->right, c, &ok, Tnone, 0);
4162 static void interp_prog(struct exec *prog, char **argv)
4164 struct binode *p = cast(binode, prog);
4171 al = cast(binode, p->left);
4173 struct var *v = cast(var, al->left);
4174 struct value *vl = v->var->val;
4176 if (argv[0] == NULL) {
4177 printf("Not enough args\n");
4180 al = cast(binode, al->right);
4182 free_value(v->var->type, vl);
4184 vl = val_alloc(v->var->type, NULL);
4187 free_value(v->var->type, vl);
4188 vl->str.len = strlen(argv[0]);
4189 vl->str.txt = malloc(vl->str.len);
4190 memcpy(vl->str.txt, argv[0], vl->str.len);
4193 v = interp_exec(p->right, &vtype);
4194 free_value(vtype, &v);
4197 ###### interp binode cases
4198 case Program: abort(); // NOTEST
4200 ## And now to test it out.
4202 Having a language requires having a "hello world" program. I'll
4203 provide a little more than that: a program that prints "Hello world"
4204 finds the GCD of two numbers, prints the first few elements of
4205 Fibonacci, performs a binary search for a number, and a few other
4206 things which will likely grow as the languages grows.
4208 ###### File: oceani.mk
4211 @echo "===== DEMO ====="
4212 ./oceani --section "demo: hello" oceani.mdc 55 33
4218 four ::= 2 + 2 ; five ::= 10/2
4219 const pie ::= "I like Pie";
4220 cake ::= "The cake is"
4229 print "Hello World, what lovely oceans you have!"
4230 print "Are there", five, "?"
4231 print pi, pie, "but", cake
4233 A := $Astr; B := $Bstr
4235 /* When a variable is defined in both branches of an 'if',
4236 * and used afterwards, the variables are merged.
4242 print "Is", A, "bigger than", B,"? ", bigger
4243 /* If a variable is not used after the 'if', no
4244 * merge happens, so types can be different
4247 double:string = "yes"
4248 print A, "is more than twice", B, "?", double
4251 print "double", B, "is", double
4256 if a > 0 and then b > 0:
4262 print "GCD of", A, "and", B,"is", a
4264 print a, "is not positive, cannot calculate GCD"
4266 print b, "is not positive, cannot calculate GCD"
4271 print "Fibonacci:", f1,f2,
4272 then togo = togo - 1
4280 /* Binary search... */
4285 mid := (lo + hi) / 2
4297 print "Yay, I found", target
4299 print "Closest I found was", mid
4304 // "middle square" PRNG. Not particularly good, but one my
4305 // Dad taught me - the first one I ever heard of.
4306 for i:=1; then i = i + 1; while i < size:
4307 n := list[i-1] * list[i-1]
4308 list[i] = (n / 100) % 10 000
4310 print "Before sort:",
4311 for i:=0; then i = i + 1; while i < size:
4315 for i := 1; then i=i+1; while i < size:
4316 for j:=i-1; then j=j-1; while j >= 0:
4317 if list[j] > list[j+1]:
4321 print " After sort:",
4322 for i:=0; then i = i + 1; while i < size:
4326 if 1 == 2 then print "yes"; else print "no"
4330 bob.alive = (bob.name == "Hello")
4331 print "bob", "is" if bob.alive else "isn't", "alive"