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 (*print)(struct type *type, struct value *val);
433 void (*print_type)(struct type *type, FILE *f);
434 int (*cmp_order)(struct type *t1, struct type *t2,
435 struct value *v1, struct value *v2);
436 int (*cmp_eq)(struct type *t1, struct type *t2,
437 struct value *v1, struct value *v2);
438 void (*dup)(struct type *type, struct value *vold, struct value *vnew);
439 void (*free)(struct type *type, struct value *val);
440 void (*free_type)(struct type *t);
441 long long (*to_int)(struct value *v);
442 double (*to_float)(struct value *v);
443 int (*to_mpq)(mpq_t *q, struct value *v);
452 struct type *typelist;
456 static struct type *find_type(struct parse_context *c, struct text s)
458 struct type *l = c->typelist;
461 text_cmp(l->name, s) != 0)
466 static struct type *add_type(struct parse_context *c, struct text s,
471 n = calloc(1, sizeof(*n));
474 n->next = c->typelist;
479 static void free_type(struct type *t)
481 /* The type is always a reference to something in the
482 * context, so we don't need to free anything.
486 static void free_value(struct type *type, struct value *v)
492 static void type_print(struct type *type, FILE *f)
495 fputs("*unknown*type*", f);
496 else if (type->name.len)
497 fprintf(f, "%.*s", type->name.len, type->name.txt);
498 else if (type->print_type)
499 type->print_type(type, f);
501 fputs("*invalid*type*", f); // NOTEST
504 static void val_init(struct type *type, struct value *val)
506 if (type && type->init)
507 type->init(type, val);
510 static void dup_value(struct type *type,
511 struct value *vold, struct value *vnew)
513 if (type && type->dup)
514 type->dup(type, vold, vnew);
517 static int value_cmp(struct type *tl, struct type *tr,
518 struct value *left, struct value *right)
520 if (tl && tl->cmp_order)
521 return tl->cmp_order(tl, tr, left, right);
522 if (tl && tl->cmp_eq)
523 return tl->cmp_eq(tl, tr, left, right);
527 static void print_value(struct type *type, struct value *v)
529 if (type && type->print)
530 type->print(type, v);
532 printf("*Unknown*"); // NOTEST
535 static struct value *val_alloc(struct type *t, struct value *init)
541 ret = calloc(1, t->size);
543 memcpy(ret, init, t->size);
551 static void free_value(struct type *type, struct value *v);
552 static int type_compat(struct type *require, struct type *have, int rules);
553 static void type_print(struct type *type, FILE *f);
554 static void val_init(struct type *type, struct value *v);
555 static void dup_value(struct type *type,
556 struct value *vold, struct value *vnew);
557 static int value_cmp(struct type *tl, struct type *tr,
558 struct value *left, struct value *right);
559 static void print_value(struct type *type, struct value *v);
561 ###### free context types
563 while (context.typelist) {
564 struct type *t = context.typelist;
566 context.typelist = t->next;
574 Values of the base types can be numbers, which we represent as
575 multi-precision fractions, strings, Booleans and labels. When
576 analysing the program we also need to allow for places where no value
577 is meaningful (type `Tnone`) and where we don't know what type to
578 expect yet (type is `NULL`).
580 Values are never shared, they are always copied when used, and freed
581 when no longer needed.
583 When propagating type information around the program, we need to
584 determine if two types are compatible, where type `NULL` is compatible
585 with anything. There are two special cases with type compatibility,
586 both related to the Conditional Statement which will be described
587 later. In some cases a Boolean can be accepted as well as some other
588 primary type, and in others any type is acceptable except a label (`Vlabel`).
589 A separate function encoding these cases will simplify some code later.
593 int (*compat)(struct type *this, struct type *other);
597 static int type_compat(struct type *require, struct type *have, int rules)
599 if ((rules & Rboolok) && have == Tbool)
601 if ((rules & Rnolabel) && have == Tlabel)
603 if (!require || !have)
607 return require->compat(require, have);
609 return require == have;
614 #include "parse_string.h"
615 #include "parse_number.h"
618 myLDLIBS := libnumber.o libstring.o -lgmp
619 LDLIBS := $(filter-out $(myLDLIBS),$(LDLIBS)) $(myLDLIBS)
621 ###### type union fields
622 enum vtype {Vnone, Vstr, Vnum, Vbool, Vlabel} vtype;
624 ###### value union fields
631 static void _free_value(struct type *type, struct value *v)
635 switch (type->vtype) {
637 case Vstr: free(v->str.txt); break;
638 case Vnum: mpq_clear(v->num); break;
644 ###### value functions
646 static void _val_init(struct type *type, struct value *val)
648 switch(type->vtype) {
649 case Vnone: // NOTEST
652 mpq_init(val->num); break;
654 val->str.txt = malloc(1);
660 case Vlabel: // NOTEST
661 val->label = NULL; // NOTEST
666 static void _dup_value(struct type *type,
667 struct value *vold, struct value *vnew)
669 switch (type->vtype) {
670 case Vnone: // NOTEST
673 vnew->label = vold->label;
676 vnew->bool = vold->bool;
680 mpq_set(vnew->num, vold->num);
683 vnew->str.len = vold->str.len;
684 vnew->str.txt = malloc(vnew->str.len);
685 memcpy(vnew->str.txt, vold->str.txt, vnew->str.len);
690 static int _value_cmp(struct type *tl, struct type *tr,
691 struct value *left, struct value *right)
695 return tl - tr; // NOTEST
697 case Vlabel: cmp = left->label == right->label ? 0 : 1; break;
698 case Vnum: cmp = mpq_cmp(left->num, right->num); break;
699 case Vstr: cmp = text_cmp(left->str, right->str); break;
700 case Vbool: cmp = left->bool - right->bool; break;
701 case Vnone: cmp = 0; // NOTEST
706 static void _print_value(struct type *type, struct value *v)
708 switch (type->vtype) {
709 case Vnone: // NOTEST
710 printf("*no-value*"); break; // NOTEST
711 case Vlabel: // NOTEST
712 printf("*label-%p*", v->label); break; // NOTEST
714 printf("%.*s", v->str.len, v->str.txt); break;
716 printf("%s", v->bool ? "True":"False"); break;
721 mpf_set_q(fl, v->num);
722 gmp_printf("%Fg", fl);
729 static void _free_value(struct type *type, struct value *v);
731 static struct type base_prototype = {
733 .print = _print_value,
734 .cmp_order = _value_cmp,
735 .cmp_eq = _value_cmp,
740 static struct type *Tbool, *Tstr, *Tnum, *Tnone, *Tlabel;
743 static struct type *add_base_type(struct parse_context *c, char *n,
744 enum vtype vt, int size)
746 struct text txt = { n, strlen(n) };
749 t = add_type(c, txt, &base_prototype);
752 t->align = size > sizeof(void*) ? sizeof(void*) : size;
753 if (t->size & (t->align - 1))
754 t->size = (t->size | (t->align - 1)) + 1;
758 ###### context initialization
760 Tbool = add_base_type(&context, "Boolean", Vbool, sizeof(char));
761 Tstr = add_base_type(&context, "string", Vstr, sizeof(struct text));
762 Tnum = add_base_type(&context, "number", Vnum, sizeof(mpq_t));
763 Tnone = add_base_type(&context, "none", Vnone, 0);
764 Tlabel = add_base_type(&context, "label", Vlabel, sizeof(void*));
768 Variables are scoped named values. We store the names in a linked list
769 of "bindings" sorted in lexical order, and use sequential search and
776 struct binding *next; // in lexical order
780 This linked list is stored in the parse context so that "reduce"
781 functions can find or add variables, and so the analysis phase can
782 ensure that every variable gets a type.
786 struct binding *varlist; // In lexical order
790 static struct binding *find_binding(struct parse_context *c, struct text s)
792 struct binding **l = &c->varlist;
797 (cmp = text_cmp((*l)->name, s)) < 0)
801 n = calloc(1, sizeof(*n));
808 Each name can be linked to multiple variables defined in different
809 scopes. Each scope starts where the name is declared and continues
810 until the end of the containing code block. Scopes of a given name
811 cannot nest, so a declaration while a name is in-scope is an error.
813 ###### binding fields
814 struct variable *var;
818 struct variable *previous;
821 struct binding *name;
822 struct exec *where_decl;// where name was declared
823 struct exec *where_set; // where type was set
827 While the naming seems strange, we include local constants in the
828 definition of variables. A name declared `var := value` can
829 subsequently be changed, but a name declared `var ::= value` cannot -
832 ###### variable fields
835 Scopes in parallel branches can be partially merged. More
836 specifically, if a given name is declared in both branches of an
837 if/else then its scope is a candidate for merging. Similarly if
838 every branch of an exhaustive switch (e.g. has an "else" clause)
839 declares a given name, then the scopes from the branches are
840 candidates for merging.
842 Note that names declared inside a loop (which is only parallel to
843 itself) are never visible after the loop. Similarly names defined in
844 scopes which are not parallel, such as those started by `for` and
845 `switch`, are never visible after the scope. Only variables defined in
846 both `then` and `else` (including the implicit then after an `if`, and
847 excluding `then` used with `for`) and in all `case`s and `else` of a
848 `switch` or `while` can be visible beyond the `if`/`switch`/`while`.
850 Labels, which are a bit like variables, follow different rules.
851 Labels are not explicitly declared, but if an undeclared name appears
852 in a context where a label is legal, that effectively declares the
853 name as a label. The declaration remains in force (or in scope) at
854 least to the end of the immediately containing block and conditionally
855 in any larger containing block which does not declare the name in some
856 other way. Importantly, the conditional scope extension happens even
857 if the label is only used in one parallel branch of a conditional --
858 when used in one branch it is treated as having been declared in all
861 Merge candidates are tentatively visible beyond the end of the
862 branching statement which creates them. If the name is used, the
863 merge is affirmed and they become a single variable visible at the
864 outer layer. If not - if it is redeclared first - the merge lapses.
866 To track scopes we have an extra stack, implemented as a linked list,
867 which roughly parallels the parse stack and which is used exclusively
868 for scoping. When a new scope is opened, a new frame is pushed and
869 the child-count of the parent frame is incremented. This child-count
870 is used to distinguish between the first of a set of parallel scopes,
871 in which declared variables must not be in scope, and subsequent
872 branches, whether they may already be conditionally scoped.
874 To push a new frame *before* any code in the frame is parsed, we need a
875 grammar reduction. This is most easily achieved with a grammar
876 element which derives the empty string, and creates the new scope when
877 it is recognised. This can be placed, for example, between a keyword
878 like "if" and the code following it.
882 struct scope *parent;
888 struct scope *scope_stack;
891 static void scope_pop(struct parse_context *c)
893 struct scope *s = c->scope_stack;
895 c->scope_stack = s->parent;
900 static void scope_push(struct parse_context *c)
902 struct scope *s = calloc(1, sizeof(*s));
904 c->scope_stack->child_count += 1;
905 s->parent = c->scope_stack;
913 OpenScope -> ${ scope_push(c); }$
914 ClosePara -> ${ var_block_close(c, CloseParallel); }$
916 Each variable records a scope depth and is in one of four states:
918 - "in scope". This is the case between the declaration of the
919 variable and the end of the containing block, and also between
920 the usage with affirms a merge and the end of that block.
922 The scope depth is not greater than the current parse context scope
923 nest depth. When the block of that depth closes, the state will
924 change. To achieve this, all "in scope" variables are linked
925 together as a stack in nesting order.
927 - "pending". The "in scope" block has closed, but other parallel
928 scopes are still being processed. So far, every parallel block at
929 the same level that has closed has declared the name.
931 The scope depth is the depth of the last parallel block that
932 enclosed the declaration, and that has closed.
934 - "conditionally in scope". The "in scope" block and all parallel
935 scopes have closed, and no further mention of the name has been
936 seen. This state includes a secondary nest depth which records the
937 outermost scope seen since the variable became conditionally in
938 scope. If a use of the name is found, the variable becomes "in
939 scope" and that secondary depth becomes the recorded scope depth.
940 If the name is declared as a new variable, the old variable becomes
941 "out of scope" and the recorded scope depth stays unchanged.
943 - "out of scope". The variable is neither in scope nor conditionally
944 in scope. It is permanently out of scope now and can be removed from
945 the "in scope" stack.
947 ###### variable fields
948 int depth, min_depth;
949 enum { OutScope, PendingScope, CondScope, InScope } scope;
950 struct variable *in_scope;
954 struct variable *in_scope;
956 All variables with the same name are linked together using the
957 'previous' link. Those variable that have been affirmatively merged all
958 have a 'merged' pointer that points to one primary variable - the most
959 recently declared instance. When merging variables, we need to also
960 adjust the 'merged' pointer on any other variables that had previously
961 been merged with the one that will no longer be primary.
963 A variable that is no longer the most recent instance of a name may
964 still have "pending" scope, if it might still be merged with most
965 recent instance. These variables don't really belong in the
966 "in_scope" list, but are not immediately removed when a new instance
967 is found. Instead, they are detected and ignored when considering the
968 list of in_scope names.
970 ###### variable fields
971 struct variable *merged;
975 static void variable_merge(struct variable *primary, struct variable *secondary)
981 primary = primary->merged;
983 for (v = primary->previous; v; v=v->previous)
984 if (v == secondary || v == secondary->merged ||
985 v->merged == secondary ||
986 (v->merged && v->merged == secondary->merged)) {
992 ###### free context vars
994 while (context.varlist) {
995 struct binding *b = context.varlist;
996 struct variable *v = b->var;
997 context.varlist = b->next;
1000 struct variable *t = v;
1003 free_value(t->type, t->val);
1006 // This is a global constant
1007 free_exec(t->where_decl);
1012 #### Manipulating Bindings
1014 When a name is conditionally visible, a new declaration discards the
1015 old binding - the condition lapses. Conversely a usage of the name
1016 affirms the visibility and extends it to the end of the containing
1017 block - i.e. the block that contains both the original declaration and
1018 the latest usage. This is determined from `min_depth`. When a
1019 conditionally visible variable gets affirmed like this, it is also
1020 merged with other conditionally visible variables with the same name.
1022 When we parse a variable declaration we either report an error if the
1023 name is currently bound, or create a new variable at the current nest
1024 depth if the name is unbound or bound to a conditionally scoped or
1025 pending-scope variable. If the previous variable was conditionally
1026 scoped, it and its homonyms becomes out-of-scope.
1028 When we parse a variable reference (including non-declarative assignment
1029 "foo = bar") we report an error if the name is not bound or is bound to
1030 a pending-scope variable; update the scope if the name is bound to a
1031 conditionally scoped variable; or just proceed normally if the named
1032 variable is in scope.
1034 When we exit a scope, any variables bound at this level are either
1035 marked out of scope or pending-scoped, depending on whether the scope
1036 was sequential or parallel. Here a "parallel" scope means the "then"
1037 or "else" part of a conditional, or any "case" or "else" branch of a
1038 switch. Other scopes are "sequential".
1040 When exiting a parallel scope we check if there are any variables that
1041 were previously pending and are still visible. If there are, then
1042 there weren't redeclared in the most recent scope, so they cannot be
1043 merged and must become out-of-scope. If it is not the first of
1044 parallel scopes (based on `child_count`), we check that there was a
1045 previous binding that is still pending-scope. If there isn't, the new
1046 variable must now be out-of-scope.
1048 When exiting a sequential scope that immediately enclosed parallel
1049 scopes, we need to resolve any pending-scope variables. If there was
1050 no `else` clause, and we cannot determine that the `switch` was exhaustive,
1051 we need to mark all pending-scope variable as out-of-scope. Otherwise
1052 all pending-scope variables become conditionally scoped.
1055 enum closetype { CloseSequential, CloseParallel, CloseElse };
1057 ###### ast functions
1059 static struct variable *var_decl(struct parse_context *c, struct text s)
1061 struct binding *b = find_binding(c, s);
1062 struct variable *v = b->var;
1064 switch (v ? v->scope : OutScope) {
1066 /* Caller will report the error */
1070 v && v->scope == CondScope;
1072 v->scope = OutScope;
1076 v = calloc(1, sizeof(*v));
1077 v->previous = b->var;
1080 v->min_depth = v->depth = c->scope_depth;
1082 v->in_scope = c->in_scope;
1088 static struct variable *var_ref(struct parse_context *c, struct text s)
1090 struct binding *b = find_binding(c, s);
1091 struct variable *v = b->var;
1092 struct variable *v2;
1094 switch (v ? v->scope : OutScope) {
1097 /* Caller will report the error */
1100 /* All CondScope variables of this name need to be merged
1101 * and become InScope
1103 v->depth = v->min_depth;
1105 for (v2 = v->previous;
1106 v2 && v2->scope == CondScope;
1108 variable_merge(v, v2);
1116 static void var_block_close(struct parse_context *c, enum closetype ct)
1118 /* Close off all variables that are in_scope */
1119 struct variable *v, **vp, *v2;
1122 for (vp = &c->in_scope;
1123 v = *vp, v && v->depth > c->scope_depth && v->min_depth > c->scope_depth;
1125 if (v->name->var == v) switch (ct) {
1127 case CloseParallel: /* handle PendingScope */
1131 if (c->scope_stack->child_count == 1)
1132 v->scope = PendingScope;
1133 else if (v->previous &&
1134 v->previous->scope == PendingScope)
1135 v->scope = PendingScope;
1136 else if (v->type == Tlabel)
1137 v->scope = PendingScope;
1138 else if (v->name->var == v)
1139 v->scope = OutScope;
1140 if (ct == CloseElse) {
1141 /* All Pending variables with this name
1142 * are now Conditional */
1144 v2 && v2->scope == PendingScope;
1146 v2->scope = CondScope;
1151 v2 && v2->scope == PendingScope;
1153 if (v2->type != Tlabel)
1154 v2->scope = OutScope;
1156 case OutScope: break;
1159 case CloseSequential:
1160 if (v->type == Tlabel)
1161 v->scope = PendingScope;
1164 v->scope = OutScope;
1167 /* There was no 'else', so we can only become
1168 * conditional if we know the cases were exhaustive,
1169 * and that doesn't mean anything yet.
1170 * So only labels become conditional..
1173 v2 && v2->scope == PendingScope;
1175 if (v2->type == Tlabel) {
1176 v2->scope = CondScope;
1177 v2->min_depth = c->scope_depth;
1179 v2->scope = OutScope;
1182 case OutScope: break;
1186 if (v->scope == OutScope || v->name->var != v)
1195 Executables can be lots of different things. In many cases an
1196 executable is just an operation combined with one or two other
1197 executables. This allows for expressions and lists etc. Other times an
1198 executable is something quite specific like a constant or variable name.
1199 So we define a `struct exec` to be a general executable with a type, and
1200 a `struct binode` which is a subclass of `exec`, forms a node in a
1201 binary tree, and holds an operation. There will be other subclasses,
1202 and to access these we need to be able to `cast` the `exec` into the
1203 various other types. The first field in any `struct exec` is the type
1204 from the `exec_types` enum.
1207 #define cast(structname, pointer) ({ \
1208 const typeof( ((struct structname *)0)->type) *__mptr = &(pointer)->type; \
1209 if (__mptr && *__mptr != X##structname) abort(); \
1210 (struct structname *)( (char *)__mptr);})
1212 #define new(structname) ({ \
1213 struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
1214 __ptr->type = X##structname; \
1215 __ptr->line = -1; __ptr->column = -1; \
1218 #define new_pos(structname, token) ({ \
1219 struct structname *__ptr = ((struct structname *)calloc(1,sizeof(struct structname))); \
1220 __ptr->type = X##structname; \
1221 __ptr->line = token.line; __ptr->column = token.col; \
1230 enum exec_types type;
1238 struct exec *left, *right;
1241 ###### ast functions
1243 static int __fput_loc(struct exec *loc, FILE *f)
1247 if (loc->line >= 0) {
1248 fprintf(f, "%d:%d: ", loc->line, loc->column);
1251 if (loc->type == Xbinode)
1252 return __fput_loc(cast(binode,loc)->left, f) ||
1253 __fput_loc(cast(binode,loc)->right, f);
1256 static void fput_loc(struct exec *loc, FILE *f)
1258 if (!__fput_loc(loc, f))
1259 fprintf(f, "??:??: "); // NOTEST
1262 Each different type of `exec` node needs a number of functions defined,
1263 a bit like methods. We must be able to free it, print it, analyse it
1264 and execute it. Once we have specific `exec` types we will need to
1265 parse them too. Let's take this a bit more slowly.
1269 The parser generator requires a `free_foo` function for each struct
1270 that stores attributes and they will often be `exec`s and subtypes
1271 there-of. So we need `free_exec` which can handle all the subtypes,
1272 and we need `free_binode`.
1274 ###### ast functions
1276 static void free_binode(struct binode *b)
1281 free_exec(b->right);
1285 ###### core functions
1286 static void free_exec(struct exec *e)
1295 ###### forward decls
1297 static void free_exec(struct exec *e);
1299 ###### free exec cases
1300 case Xbinode: free_binode(cast(binode, e)); break;
1304 Printing an `exec` requires that we know the current indent level for
1305 printing line-oriented components. As will become clear later, we
1306 also want to know what sort of bracketing to use.
1308 ###### ast functions
1310 static void do_indent(int i, char *str)
1317 ###### core functions
1318 static void print_binode(struct binode *b, int indent, int bracket)
1322 ## print binode cases
1326 static void print_exec(struct exec *e, int indent, int bracket)
1332 print_binode(cast(binode, e), indent, bracket); break;
1337 ###### forward decls
1339 static void print_exec(struct exec *e, int indent, int bracket);
1343 As discussed, analysis involves propagating type requirements around the
1344 program and looking for errors.
1346 So `propagate_types` is passed an expected type (being a `struct type`
1347 pointer together with some `val_rules` flags) that the `exec` is
1348 expected to return, and returns the type that it does return, either
1349 of which can be `NULL` signifying "unknown". An `ok` flag is passed
1350 by reference. It is set to `0` when an error is found, and `2` when
1351 any change is made. If it remains unchanged at `1`, then no more
1352 propagation is needed.
1356 enum val_rules {Rnolabel = 1<<0, Rboolok = 1<<1, Rnoconstant = 2<<1};
1360 if (rules & Rnolabel)
1361 fputs(" (labels not permitted)", stderr);
1364 ###### core functions
1366 static struct type *propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1367 struct type *type, int rules);
1368 static struct type *__propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1369 struct type *type, int rules)
1376 switch (prog->type) {
1379 struct binode *b = cast(binode, prog);
1381 ## propagate binode cases
1385 ## propagate exec cases
1390 static struct type *propagate_types(struct exec *prog, struct parse_context *c, int *ok,
1391 struct type *type, int rules)
1393 struct type *ret = __propagate_types(prog, c, ok, type, rules);
1402 Interpreting an `exec` doesn't require anything but the `exec`. State
1403 is stored in variables and each variable will be directly linked from
1404 within the `exec` tree. The exception to this is the whole `program`
1405 which needs to look at command line arguments. The `program` will be
1406 interpreted separately.
1408 Each `exec` can return a value combined with a type in `struct lrval`.
1409 The type may be `Tnone` but must be non-NULL. Some `exec`s will return
1410 the location of a value, which can be updated, in `lval`. Others will
1411 set `lval` to NULL indicating that there is a value of appropriate type
1415 ###### core functions
1419 struct value rval, *lval;
1422 static struct lrval _interp_exec(struct exec *e);
1424 static struct value interp_exec(struct exec *e, struct type **typeret)
1426 struct lrval ret = _interp_exec(e);
1428 if (!ret.type) abort();
1430 *typeret = ret.type;
1432 dup_value(ret.type, ret.lval, &ret.rval);
1436 static struct value *linterp_exec(struct exec *e, struct type **typeret)
1438 struct lrval ret = _interp_exec(e);
1441 *typeret = ret.type;
1443 free_value(ret.type, &ret.rval);
1447 static struct lrval _interp_exec(struct exec *e)
1450 struct value rv = {}, *lrv = NULL;
1451 struct type *rvtype;
1453 rvtype = ret.type = Tnone;
1463 struct binode *b = cast(binode, e);
1464 struct value left, right, *lleft;
1465 struct type *ltype, *rtype;
1466 ltype = rtype = Tnone;
1468 ## interp binode cases
1470 free_value(ltype, &left);
1471 free_value(rtype, &right);
1474 ## interp exec cases
1484 Now that we have the shape of the interpreter in place we can add some
1485 complex types and connected them in to the data structures and the
1486 different phases of parse, analyse, print, interpret.
1488 Thus far we have arrays and structs.
1492 Arrays can be declared by giving a size and a type, as `[size]type' so
1493 `freq:[26]number` declares `freq` to be an array of 26 numbers. The
1494 size can be either a literal number, or a named constant. Some day an
1495 arbitrary expression will be supported.
1497 Arrays cannot be assigned. When pointers are introduced we will also
1498 introduce array slices which can refer to part or all of an array -
1499 the assignment syntax will create a slice. For now, an array can only
1500 ever be referenced by the name it is declared with. It is likely that
1501 a "`copy`" primitive will eventually be define which can be used to
1502 make a copy of an array with controllable recursive depth.
1504 ###### type union fields
1508 struct variable *vsize;
1509 struct type *member;
1512 ###### value functions
1514 static void array_init(struct type *type, struct value *val)
1518 if (type->array.vsize) {
1521 mpz_tdiv_q(q, mpq_numref(type->array.vsize->val->num),
1522 mpq_denref(type->array.vsize->val->num));
1523 type->array.size = mpz_get_si(q);
1526 type->size = type->array.size * type->array.member->size;
1527 type->align = type->array.member->align;
1531 for (i = 0; i < type->array.size; i++) {
1533 v = (void*)val->ptr + i * type->array.member->size;
1534 val_init(type->array.member, v);
1538 static void array_free(struct type *type, struct value *val)
1542 for (i = 0; i < type->array.size; i++) {
1544 v = (void*)val->ptr + i * type->array.member->size;
1545 free_value(type->array.member, v);
1549 static int array_compat(struct type *require, struct type *have)
1551 if (have->compat != require->compat)
1553 /* Both are arrays, so we can look at details */
1554 if (!type_compat(require->array.member, have->array.member, 0))
1556 if (require->array.vsize == NULL && have->array.vsize == NULL)
1557 return require->array.size == have->array.size;
1559 return require->array.vsize == have->array.vsize;
1562 static void array_print_type(struct type *type, FILE *f)
1565 if (type->array.vsize) {
1566 struct binding *b = type->array.vsize->name;
1567 fprintf(f, "%.*s]", b->name.len, b->name.txt);
1569 fprintf(f, "%d]", type->array.size);
1570 type_print(type->array.member, f);
1573 static struct type array_prototype = {
1575 .print_type = array_print_type,
1576 .compat = array_compat,
1580 ###### declare terminals
1585 | [ NUMBER ] Type ${ {
1588 struct text noname = { "", 0 };
1590 $0 = add_type(c, noname, &array_prototype);
1591 $0->array.member = $<4;
1592 $0->array.vsize = NULL;
1593 if (number_parse(num, tail, $2.txt) == 0)
1594 tok_err(c, "error: unrecognised number", &$2);
1596 tok_err(c, "error: unsupported number suffix", &$2);
1598 $0->array.size = mpz_get_ui(mpq_numref(num));
1599 if (mpz_cmp_ui(mpq_denref(num), 1) != 0) {
1600 tok_err(c, "error: array size must be an integer",
1602 } else if (mpz_cmp_ui(mpq_numref(num), 1UL << 30) >= 0)
1603 tok_err(c, "error: array size is too large",
1609 | [ IDENTIFIER ] Type ${ {
1610 struct variable *v = var_ref(c, $2.txt);
1611 struct text noname = { "", 0 };
1614 tok_err(c, "error: name undeclared", &$2);
1615 else if (!v->constant)
1616 tok_err(c, "error: array size must be a constant", &$2);
1618 $0 = add_type(c, noname, &array_prototype);
1619 $0->array.member = $<4;
1621 $0->array.vsize = v;
1627 ###### variable grammar
1629 | Variable [ Expression ] ${ {
1630 struct binode *b = new(binode);
1637 ###### print binode cases
1639 print_exec(b->left, -1, bracket);
1641 print_exec(b->right, -1, bracket);
1645 ###### propagate binode cases
1647 /* left must be an array, right must be a number,
1648 * result is the member type of the array
1650 propagate_types(b->right, c, ok, Tnum, 0);
1651 t = propagate_types(b->left, c, ok, NULL, rules & Rnoconstant);
1652 if (!t || t->compat != array_compat) {
1653 type_err(c, "error: %1 cannot be indexed", prog, t, 0, NULL);
1656 if (!type_compat(type, t->array.member, rules)) {
1657 type_err(c, "error: have %1 but need %2", prog,
1658 t->array.member, rules, type);
1660 return t->array.member;
1664 ###### interp binode cases
1669 lleft = linterp_exec(b->left, <ype);
1670 right = interp_exec(b->right, &rtype);
1672 mpz_tdiv_q(q, mpq_numref(right.num), mpq_denref(right.num));
1676 rvtype = ltype->array.member;
1677 if (i >= 0 && i < ltype->array.size)
1678 lrv = (void*)lleft + i * rvtype->size;
1680 val_init(ltype->array.member, &rv);
1687 A `struct` is a data-type that contains one or more other data-types.
1688 It differs from an array in that each member can be of a different
1689 type, and they are accessed by name rather than by number. Thus you
1690 cannot choose an element by calculation, you need to know what you
1693 The language makes no promises about how a given structure will be
1694 stored in memory - it is free to rearrange fields to suit whatever
1695 criteria seems important.
1697 Structs are declared separately from program code - they cannot be
1698 declared in-line in a variable declaration like arrays can. A struct
1699 is given a name and this name is used to identify the type - the name
1700 is not prefixed by the word `struct` as it would be in C.
1702 Structs are only treated as the same if they have the same name.
1703 Simply having the same fields in the same order is not enough. This
1704 might change once we can create structure initializers from a list of
1707 Each component datum is identified much like a variable is declared,
1708 with a name, one or two colons, and a type. The type cannot be omitted
1709 as there is no opportunity to deduce the type from usage. An initial
1710 value can be given following an equals sign, so
1712 ##### Example: a struct type
1718 would declare a type called "complex" which has two number fields,
1719 each initialised to zero.
1721 Struct will need to be declared separately from the code that uses
1722 them, so we will need to be able to print out the declaration of a
1723 struct when reprinting the whole program. So a `print_type_decl` type
1724 function will be needed.
1726 ###### type union fields
1738 ###### type functions
1739 void (*print_type_decl)(struct type *type, FILE *f);
1741 ###### value functions
1743 static void structure_init(struct type *type, struct value *val)
1747 for (i = 0; i < type->structure.nfields; i++) {
1749 v = (void*) val->ptr + type->structure.fields[i].offset;
1750 val_init(type->structure.fields[i].type, v);
1754 static void structure_free(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 free_value(type->structure.fields[i].type, v);
1765 static void structure_free_type(struct type *t)
1768 for (i = 0; i < t->structure.nfields; i++)
1769 if (t->structure.fields[i].init) {
1770 free_value(t->structure.fields[i].type,
1771 t->structure.fields[i].init);
1772 free(t->structure.fields[i].init);
1774 free(t->structure.fields);
1777 static struct type structure_prototype = {
1778 .init = structure_init,
1779 .free = structure_free,
1780 .free_type = structure_free_type,
1781 .print_type_decl = structure_print_type,
1795 ###### free exec cases
1797 free_exec(cast(fieldref, e)->left);
1801 ###### declare terminals
1804 ###### variable grammar
1806 | Variable . IDENTIFIER ${ {
1807 struct fieldref *fr = new_pos(fieldref, $2);
1814 ###### print exec cases
1818 struct fieldref *f = cast(fieldref, e);
1819 print_exec(f->left, -1, bracket);
1820 printf(".%.*s", f->name.len, f->name.txt);
1824 ###### ast functions
1825 static int find_struct_index(struct type *type, struct text field)
1828 for (i = 0; i < type->structure.nfields; i++)
1829 if (text_cmp(type->structure.fields[i].name, field) == 0)
1834 ###### propagate exec cases
1838 struct fieldref *f = cast(fieldref, prog);
1839 struct type *st = propagate_types(f->left, c, ok, NULL, 0);
1842 type_err(c, "error: unknown type for field access", f->left,
1844 else if (st->init != structure_init)
1845 type_err(c, "error: field reference attempted on %1, not a struct",
1846 f->left, st, 0, NULL);
1847 else if (f->index == -2) {
1848 f->index = find_struct_index(st, f->name);
1850 type_err(c, "error: cannot find requested field in %1",
1851 f->left, st, 0, NULL);
1853 if (f->index >= 0) {
1854 struct type *ft = st->structure.fields[f->index].type;
1855 if (!type_compat(type, ft, rules))
1856 type_err(c, "error: have %1 but need %2", prog,
1863 ###### interp exec cases
1866 struct fieldref *f = cast(fieldref, e);
1868 struct value *lleft = linterp_exec(f->left, <ype);
1869 lrv = (void*)lleft->ptr + ltype->structure.fields[f->index].offset;
1870 rvtype = ltype->structure.fields[f->index].type;
1876 struct fieldlist *prev;
1880 ###### ast functions
1881 static void free_fieldlist(struct fieldlist *f)
1885 free_fieldlist(f->prev);
1887 free_value(f->f.type, f->f.init);
1893 ###### top level grammar
1894 DeclareStruct -> struct IDENTIFIER FieldBlock Newlines ${ {
1896 add_type(c, $2.txt, &structure_prototype);
1898 struct fieldlist *f;
1900 for (f = $3; f; f=f->prev)
1903 t->structure.nfields = cnt;
1904 t->structure.fields = calloc(cnt, sizeof(struct field));
1907 int a = f->f.type->align;
1909 t->structure.fields[cnt] = f->f;
1910 if (t->size & (a-1))
1911 t->size = (t->size | (a-1)) + 1;
1912 t->structure.fields[cnt].offset = t->size;
1913 t->size += ((f->f.type->size - 1) | (a-1)) + 1;
1922 FieldBlock -> { IN OptNL FieldLines OUT OptNL } ${ $0 = $<FL; }$
1923 | { SimpleFieldList } ${ $0 = $<SFL; }$
1924 | IN OptNL FieldLines OUT ${ $0 = $<FL; }$
1925 | SimpleFieldList EOL ${ $0 = $<SFL; }$
1927 FieldLines -> SimpleFieldList Newlines ${ $0 = $<SFL; }$
1928 | FieldLines SimpleFieldList Newlines ${
1933 SimpleFieldList -> Field ${ $0 = $<F; }$
1934 | SimpleFieldList ; Field ${
1938 | SimpleFieldList ; ${
1941 | ERROR ${ tok_err(c, "Syntax error in struct field", &$1); }$
1943 Field -> IDENTIFIER : Type = Expression ${ {
1946 $0 = calloc(1, sizeof(struct fieldlist));
1947 $0->f.name = $1.txt;
1952 propagate_types($<5, c, &ok, $3, 0);
1957 struct value vl = interp_exec($5, NULL);
1958 $0->f.init = val_alloc($0->f.type, &vl);
1961 | IDENTIFIER : Type ${
1962 $0 = calloc(1, sizeof(struct fieldlist));
1963 $0->f.name = $1.txt;
1965 $0->f.init = val_alloc($0->f.type, NULL);
1968 ###### forward decls
1969 static void structure_print_type(struct type *t, FILE *f);
1971 ###### value functions
1972 static void structure_print_type(struct type *t, FILE *f)
1976 fprintf(f, "struct %.*s\n", t->name.len, t->name.txt);
1978 for (i = 0; i < t->structure.nfields; i++) {
1979 struct field *fl = t->structure.fields + i;
1980 fprintf(f, " %.*s : ", fl->name.len, fl->name.txt);
1981 type_print(fl->type, f);
1982 if (fl->type->print && fl->init) {
1984 if (fl->type == Tstr)
1986 print_value(fl->type, fl->init);
1987 if (fl->type == Tstr)
1994 ###### print type decls
1999 while (target != 0) {
2001 for (t = context.typelist; t ; t=t->next)
2002 if (t->print_type_decl) {
2011 t->print_type_decl(t, stdout);
2017 ## Executables: the elements of code
2019 Each code element needs to be parsed, printed, analysed,
2020 interpreted, and freed. There are several, so let's just start with
2021 the easy ones and work our way up.
2025 We have already met values as separate objects. When manifest
2026 constants appear in the program text, that must result in an executable
2027 which has a constant value. So the `val` structure embeds a value in
2040 ###### ast functions
2041 struct val *new_val(struct type *T, struct token tk)
2043 struct val *v = new_pos(val, tk);
2054 $0 = new_val(Tbool, $1);
2058 $0 = new_val(Tbool, $1);
2062 $0 = new_val(Tnum, $1);
2065 if (number_parse($0->val.num, tail, $1.txt) == 0)
2066 mpq_init($0->val.num);
2068 tok_err(c, "error: unsupported number suffix",
2073 $0 = new_val(Tstr, $1);
2076 string_parse(&$1, '\\', &$0->val.str, tail);
2078 tok_err(c, "error: unsupported string suffix",
2083 $0 = new_val(Tstr, $1);
2086 string_parse(&$1, '\\', &$0->val.str, tail);
2088 tok_err(c, "error: unsupported string suffix",
2093 ###### print exec cases
2096 struct val *v = cast(val, e);
2097 if (v->vtype == Tstr)
2099 print_value(v->vtype, &v->val);
2100 if (v->vtype == Tstr)
2105 ###### propagate exec cases
2108 struct val *val = cast(val, prog);
2109 if (!type_compat(type, val->vtype, rules))
2110 type_err(c, "error: expected %1%r found %2",
2111 prog, type, rules, val->vtype);
2115 ###### interp exec cases
2117 rvtype = cast(val, e)->vtype;
2118 dup_value(rvtype, &cast(val, e)->val, &rv);
2121 ###### ast functions
2122 static void free_val(struct val *v)
2125 free_value(v->vtype, &v->val);
2129 ###### free exec cases
2130 case Xval: free_val(cast(val, e)); break;
2132 ###### ast functions
2133 // Move all nodes from 'b' to 'rv', reversing their order.
2134 // In 'b' 'left' is a list, and 'right' is the last node.
2135 // In 'rv', left' is the first node and 'right' is a list.
2136 static struct binode *reorder_bilist(struct binode *b)
2138 struct binode *rv = NULL;
2141 struct exec *t = b->right;
2145 b = cast(binode, b->left);
2155 Just as we used a `val` to wrap a value into an `exec`, we similarly
2156 need a `var` to wrap a `variable` into an exec. While each `val`
2157 contained a copy of the value, each `var` holds a link to the variable
2158 because it really is the same variable no matter where it appears.
2159 When a variable is used, we need to remember to follow the `->merged`
2160 link to find the primary instance.
2168 struct variable *var;
2176 VariableDecl -> IDENTIFIER : ${ {
2177 struct variable *v = var_decl(c, $1.txt);
2178 $0 = new_pos(var, $1);
2183 v = var_ref(c, $1.txt);
2185 type_err(c, "error: variable '%v' redeclared",
2187 type_err(c, "info: this is where '%v' was first declared",
2188 v->where_decl, NULL, 0, NULL);
2191 | IDENTIFIER :: ${ {
2192 struct variable *v = var_decl(c, $1.txt);
2193 $0 = new_pos(var, $1);
2199 v = var_ref(c, $1.txt);
2201 type_err(c, "error: variable '%v' redeclared",
2203 type_err(c, "info: this is where '%v' was first declared",
2204 v->where_decl, NULL, 0, NULL);
2207 | IDENTIFIER : Type ${ {
2208 struct variable *v = var_decl(c, $1.txt);
2209 $0 = new_pos(var, $1);
2217 v = var_ref(c, $1.txt);
2219 type_err(c, "error: variable '%v' redeclared",
2221 type_err(c, "info: this is where '%v' was first declared",
2222 v->where_decl, NULL, 0, NULL);
2225 | IDENTIFIER :: Type ${ {
2226 struct variable *v = var_decl(c, $1.txt);
2227 $0 = new_pos(var, $1);
2236 v = var_ref(c, $1.txt);
2238 type_err(c, "error: variable '%v' redeclared",
2240 type_err(c, "info: this is where '%v' was first declared",
2241 v->where_decl, NULL, 0, NULL);
2246 Variable -> IDENTIFIER ${ {
2247 struct variable *v = var_ref(c, $1.txt);
2248 $0 = new_pos(var, $1);
2250 /* This might be a label - allocate a var just in case */
2251 v = var_decl(c, $1.txt);
2259 cast(var, $0)->var = v;
2264 Type -> IDENTIFIER ${
2265 $0 = find_type(c, $1.txt);
2268 "error: undefined type", &$1);
2275 ###### print exec cases
2278 struct var *v = cast(var, e);
2280 struct binding *b = v->var->name;
2281 printf("%.*s", b->name.len, b->name.txt);
2288 if (loc->type == Xvar) {
2289 struct var *v = cast(var, loc);
2291 struct binding *b = v->var->name;
2292 fprintf(stderr, "%.*s", b->name.len, b->name.txt);
2294 fputs("???", stderr); // NOTEST
2296 fputs("NOTVAR", stderr); // NOTEST
2299 ###### propagate exec cases
2303 struct var *var = cast(var, prog);
2304 struct variable *v = var->var;
2306 type_err(c, "%d:BUG: no variable!!", prog, NULL, 0, NULL); // NOTEST
2307 return Tnone; // NOTEST
2311 if (v->constant && (rules & Rnoconstant)) {
2312 type_err(c, "error: Cannot assign to a constant: %v",
2313 prog, NULL, 0, NULL);
2314 type_err(c, "info: name was defined as a constant here",
2315 v->where_decl, NULL, 0, NULL);
2318 if (v->type == Tnone && v->where_decl == prog)
2319 type_err(c, "error: variable used but not declared: %v",
2320 prog, NULL, 0, NULL);
2321 if (v->type == NULL) {
2322 if (type && *ok != 0) {
2325 v->where_set = prog;
2330 if (!type_compat(type, v->type, rules)) {
2331 type_err(c, "error: expected %1%r but variable '%v' is %2", prog,
2332 type, rules, v->type);
2333 type_err(c, "info: this is where '%v' was set to %1", v->where_set,
2334 v->type, rules, NULL);
2341 ###### interp exec cases
2344 struct var *var = cast(var, e);
2345 struct variable *v = var->var;
2354 ###### ast functions
2356 static void free_var(struct var *v)
2361 ###### free exec cases
2362 case Xvar: free_var(cast(var, e)); break;
2364 ### Expressions: Conditional
2366 Our first user of the `binode` will be conditional expressions, which
2367 is a bit odd as they actually have three components. That will be
2368 handled by having 2 binodes for each expression. The conditional
2369 expression is the lowest precedence operator which is why we define it
2370 first - to start the precedence list.
2372 Conditional expressions are of the form "value `if` condition `else`
2373 other_value". They associate to the right, so everything to the right
2374 of `else` is part of an else value, while only a higher-precedence to
2375 the left of `if` is the if values. Between `if` and `else` there is no
2376 room for ambiguity, so a full conditional expression is allowed in
2388 Expression -> Expression if Expression else Expression $$ifelse ${ {
2389 struct binode *b1 = new(binode);
2390 struct binode *b2 = new(binode);
2399 ## expression grammar
2401 ###### print binode cases
2404 b2 = cast(binode, b->right);
2405 if (bracket) printf("(");
2406 print_exec(b2->left, -1, bracket);
2408 print_exec(b->left, -1, bracket);
2410 print_exec(b2->right, -1, bracket);
2411 if (bracket) printf(")");
2414 ###### propagate binode cases
2417 /* cond must be Tbool, others must match */
2418 struct binode *b2 = cast(binode, b->right);
2421 propagate_types(b->left, c, ok, Tbool, 0);
2422 t = propagate_types(b2->left, c, ok, type, Rnolabel);
2423 t2 = propagate_types(b2->right, c, ok, type ?: t, Rnolabel);
2427 ###### interp binode cases
2430 struct binode *b2 = cast(binode, b->right);
2431 left = interp_exec(b->left, <ype);
2433 rv = interp_exec(b2->left, &rvtype);
2435 rv = interp_exec(b2->right, &rvtype);
2439 ### Expressions: Boolean
2441 The next class of expressions to use the `binode` will be Boolean
2442 expressions. "`and then`" and "`or else`" are similar to `and` and `or`
2443 have same corresponding precendence. The difference is that they don't
2444 evaluate the second expression if not necessary.
2453 ###### expr precedence
2458 ###### expression grammar
2459 | Expression or Expression ${ {
2460 struct binode *b = new(binode);
2466 | Expression or else Expression ${ {
2467 struct binode *b = new(binode);
2474 | Expression and Expression ${ {
2475 struct binode *b = new(binode);
2481 | Expression and then Expression ${ {
2482 struct binode *b = new(binode);
2489 | not Expression ${ {
2490 struct binode *b = new(binode);
2496 ###### print binode cases
2498 if (bracket) printf("(");
2499 print_exec(b->left, -1, bracket);
2501 print_exec(b->right, -1, bracket);
2502 if (bracket) printf(")");
2505 if (bracket) printf("(");
2506 print_exec(b->left, -1, bracket);
2507 printf(" and then ");
2508 print_exec(b->right, -1, bracket);
2509 if (bracket) printf(")");
2512 if (bracket) printf("(");
2513 print_exec(b->left, -1, bracket);
2515 print_exec(b->right, -1, bracket);
2516 if (bracket) printf(")");
2519 if (bracket) printf("(");
2520 print_exec(b->left, -1, bracket);
2521 printf(" or else ");
2522 print_exec(b->right, -1, bracket);
2523 if (bracket) printf(")");
2526 if (bracket) printf("(");
2528 print_exec(b->right, -1, bracket);
2529 if (bracket) printf(")");
2532 ###### propagate binode cases
2538 /* both must be Tbool, result is Tbool */
2539 propagate_types(b->left, c, ok, Tbool, 0);
2540 propagate_types(b->right, c, ok, Tbool, 0);
2541 if (type && type != Tbool)
2542 type_err(c, "error: %1 operation found where %2 expected", prog,
2546 ###### interp binode cases
2548 rv = interp_exec(b->left, &rvtype);
2549 right = interp_exec(b->right, &rtype);
2550 rv.bool = rv.bool && right.bool;
2553 rv = interp_exec(b->left, &rvtype);
2555 rv = interp_exec(b->right, NULL);
2558 rv = interp_exec(b->left, &rvtype);
2559 right = interp_exec(b->right, &rtype);
2560 rv.bool = rv.bool || right.bool;
2563 rv = interp_exec(b->left, &rvtype);
2565 rv = interp_exec(b->right, NULL);
2568 rv = interp_exec(b->right, &rvtype);
2572 ### Expressions: Comparison
2574 Of slightly higher precedence that Boolean expressions are Comparisons.
2575 A comparison takes arguments of any comparable type, but the two types
2578 To simplify the parsing we introduce an `eop` which can record an
2579 expression operator, and the `CMPop` non-terminal will match one of them.
2586 ###### ast functions
2587 static void free_eop(struct eop *e)
2601 ###### expr precedence
2602 $LEFT < > <= >= == != CMPop
2604 ###### expression grammar
2605 | Expression CMPop Expression ${ {
2606 struct binode *b = new(binode);
2616 CMPop -> < ${ $0.op = Less; }$
2617 | > ${ $0.op = Gtr; }$
2618 | <= ${ $0.op = LessEq; }$
2619 | >= ${ $0.op = GtrEq; }$
2620 | == ${ $0.op = Eql; }$
2621 | != ${ $0.op = NEql; }$
2623 ###### print binode cases
2631 if (bracket) printf("(");
2632 print_exec(b->left, -1, bracket);
2634 case Less: printf(" < "); break;
2635 case LessEq: printf(" <= "); break;
2636 case Gtr: printf(" > "); break;
2637 case GtrEq: printf(" >= "); break;
2638 case Eql: printf(" == "); break;
2639 case NEql: printf(" != "); break;
2640 default: abort(); // NOTEST
2642 print_exec(b->right, -1, bracket);
2643 if (bracket) printf(")");
2646 ###### propagate binode cases
2653 /* Both must match but not be labels, result is Tbool */
2654 t = propagate_types(b->left, c, ok, NULL, Rnolabel);
2656 propagate_types(b->right, c, ok, t, 0);
2658 t = propagate_types(b->right, c, ok, NULL, Rnolabel);
2660 t = propagate_types(b->left, c, ok, t, 0);
2662 if (!type_compat(type, Tbool, 0))
2663 type_err(c, "error: Comparison returns %1 but %2 expected", prog,
2664 Tbool, rules, type);
2667 ###### interp binode cases
2676 left = interp_exec(b->left, <ype);
2677 right = interp_exec(b->right, &rtype);
2678 cmp = value_cmp(ltype, rtype, &left, &right);
2681 case Less: rv.bool = cmp < 0; break;
2682 case LessEq: rv.bool = cmp <= 0; break;
2683 case Gtr: rv.bool = cmp > 0; break;
2684 case GtrEq: rv.bool = cmp >= 0; break;
2685 case Eql: rv.bool = cmp == 0; break;
2686 case NEql: rv.bool = cmp != 0; break;
2687 default: rv.bool = 0; break; // NOTEST
2692 ### Expressions: The rest
2694 The remaining expressions with the highest precedence are arithmetic,
2695 string concatenation, and string conversion. String concatenation
2696 (`++`) has the same precedence as multiplication and division, but lower
2699 String conversion is a temporary feature until I get a better type
2700 system. `$` is a prefix operator which expects a string and returns
2703 `+` and `-` are both infix and prefix operations (where they are
2704 absolute value and negation). These have different operator names.
2706 We also have a 'Bracket' operator which records where parentheses were
2707 found. This makes it easy to reproduce these when printing. Possibly I
2708 should only insert brackets were needed for precedence.
2718 ###### expr precedence
2724 ###### expression grammar
2725 | Expression Eop Expression ${ {
2726 struct binode *b = new(binode);
2733 | Expression Top Expression ${ {
2734 struct binode *b = new(binode);
2741 | ( Expression ) ${ {
2742 struct binode *b = new_pos(binode, $1);
2747 | Uop Expression ${ {
2748 struct binode *b = new(binode);
2753 | Value ${ $0 = $<1; }$
2754 | Variable ${ $0 = $<1; }$
2757 Eop -> + ${ $0.op = Plus; }$
2758 | - ${ $0.op = Minus; }$
2760 Uop -> + ${ $0.op = Absolute; }$
2761 | - ${ $0.op = Negate; }$
2762 | $ ${ $0.op = StringConv; }$
2764 Top -> * ${ $0.op = Times; }$
2765 | / ${ $0.op = Divide; }$
2766 | % ${ $0.op = Rem; }$
2767 | ++ ${ $0.op = Concat; }$
2769 ###### print binode cases
2776 if (bracket) printf("(");
2777 print_exec(b->left, indent, bracket);
2779 case Plus: fputs(" + ", stdout); break;
2780 case Minus: fputs(" - ", stdout); break;
2781 case Times: fputs(" * ", stdout); break;
2782 case Divide: fputs(" / ", stdout); break;
2783 case Rem: fputs(" % ", stdout); break;
2784 case Concat: fputs(" ++ ", stdout); break;
2785 default: abort(); // NOTEST
2787 print_exec(b->right, indent, bracket);
2788 if (bracket) printf(")");
2793 if (bracket) printf("(");
2795 case Absolute: fputs("+", stdout); break;
2796 case Negate: fputs("-", stdout); break;
2797 case StringConv: fputs("$", stdout); break;
2798 default: abort(); // NOTEST
2800 print_exec(b->right, indent, bracket);
2801 if (bracket) printf(")");
2805 print_exec(b->right, indent, bracket);
2809 ###### propagate binode cases
2815 /* both must be numbers, result is Tnum */
2818 /* as propagate_types ignores a NULL,
2819 * unary ops fit here too */
2820 propagate_types(b->left, c, ok, Tnum, 0);
2821 propagate_types(b->right, c, ok, Tnum, 0);
2822 if (!type_compat(type, Tnum, 0))
2823 type_err(c, "error: Arithmetic returns %1 but %2 expected", prog,
2828 /* both must be Tstr, result is Tstr */
2829 propagate_types(b->left, c, ok, Tstr, 0);
2830 propagate_types(b->right, c, ok, Tstr, 0);
2831 if (!type_compat(type, Tstr, 0))
2832 type_err(c, "error: Concat returns %1 but %2 expected", prog,
2837 /* op must be string, result is number */
2838 propagate_types(b->left, c, ok, Tstr, 0);
2839 if (!type_compat(type, Tnum, 0))
2841 "error: Can only convert string to number, not %1",
2842 prog, type, 0, NULL);
2846 return propagate_types(b->right, c, ok, type, 0);
2848 ###### interp binode cases
2851 rv = interp_exec(b->left, &rvtype);
2852 right = interp_exec(b->right, &rtype);
2853 mpq_add(rv.num, rv.num, right.num);
2856 rv = interp_exec(b->left, &rvtype);
2857 right = interp_exec(b->right, &rtype);
2858 mpq_sub(rv.num, rv.num, right.num);
2861 rv = interp_exec(b->left, &rvtype);
2862 right = interp_exec(b->right, &rtype);
2863 mpq_mul(rv.num, rv.num, right.num);
2866 rv = interp_exec(b->left, &rvtype);
2867 right = interp_exec(b->right, &rtype);
2868 mpq_div(rv.num, rv.num, right.num);
2873 left = interp_exec(b->left, <ype);
2874 right = interp_exec(b->right, &rtype);
2875 mpz_init(l); mpz_init(r); mpz_init(rem);
2876 mpz_tdiv_q(l, mpq_numref(left.num), mpq_denref(left.num));
2877 mpz_tdiv_q(r, mpq_numref(right.num), mpq_denref(right.num));
2878 mpz_tdiv_r(rem, l, r);
2879 val_init(Tnum, &rv);
2880 mpq_set_z(rv.num, rem);
2881 mpz_clear(r); mpz_clear(l); mpz_clear(rem);
2886 rv = interp_exec(b->right, &rvtype);
2887 mpq_neg(rv.num, rv.num);
2890 rv = interp_exec(b->right, &rvtype);
2891 mpq_abs(rv.num, rv.num);
2894 rv = interp_exec(b->right, &rvtype);
2897 left = interp_exec(b->left, <ype);
2898 right = interp_exec(b->right, &rtype);
2900 rv.str = text_join(left.str, right.str);
2903 right = interp_exec(b->right, &rvtype);
2907 struct text tx = right.str;
2910 if (tx.txt[0] == '-') {
2915 if (number_parse(rv.num, tail, tx) == 0)
2918 mpq_neg(rv.num, rv.num);
2920 printf("Unsupported suffix: %.*s\n", tx.len, tx.txt);
2924 ###### value functions
2926 static struct text text_join(struct text a, struct text b)
2929 rv.len = a.len + b.len;
2930 rv.txt = malloc(rv.len);
2931 memcpy(rv.txt, a.txt, a.len);
2932 memcpy(rv.txt+a.len, b.txt, b.len);
2936 ### Blocks, Statements, and Statement lists.
2938 Now that we have expressions out of the way we need to turn to
2939 statements. There are simple statements and more complex statements.
2940 Simple statements do not contain (syntactic) newlines, complex statements do.
2942 Statements often come in sequences and we have corresponding simple
2943 statement lists and complex statement lists.
2944 The former comprise only simple statements separated by semicolons.
2945 The later comprise complex statements and simple statement lists. They are
2946 separated by newlines. Thus the semicolon is only used to separate
2947 simple statements on the one line. This may be overly restrictive,
2948 but I'm not sure I ever want a complex statement to share a line with
2951 Note that a simple statement list can still use multiple lines if
2952 subsequent lines are indented, so
2954 ###### Example: wrapped simple statement list
2959 is a single simple statement list. This might allow room for
2960 confusion, so I'm not set on it yet.
2962 A simple statement list needs no extra syntax. A complex statement
2963 list has two syntactic forms. It can be enclosed in braces (much like
2964 C blocks), or it can be introduced by an indent and continue until an
2965 unindented newline (much like Python blocks). With this extra syntax
2966 it is referred to as a block.
2968 Note that a block does not have to include any newlines if it only
2969 contains simple statements. So both of:
2971 if condition: a=b; d=f
2973 if condition { a=b; print f }
2977 In either case the list is constructed from a `binode` list with
2978 `Block` as the operator. When parsing the list it is most convenient
2979 to append to the end, so a list is a list and a statement. When using
2980 the list it is more convenient to consider a list to be a statement
2981 and a list. So we need a function to re-order a list.
2982 `reorder_bilist` serves this purpose.
2984 The only stand-alone statement we introduce at this stage is `pass`
2985 which does nothing and is represented as a `NULL` pointer in a `Block`
2986 list. Other stand-alone statements will follow once the infrastructure
2997 Block -> { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
2998 | { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
2999 | SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3000 | SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3001 | IN OptNL Statementlist OUT ${ $0 = $<Sl; }$
3003 OpenBlock -> OpenScope { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3004 | OpenScope { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3005 | OpenScope SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3006 | OpenScope SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3007 | IN OpenScope OptNL Statementlist OUT ${ $0 = $<Sl; }$
3009 UseBlock -> { OpenScope IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3010 | { OpenScope SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3011 | IN OpenScope OptNL Statementlist OUT ${ $0 = $<Sl; }$
3013 ColonBlock -> { IN OptNL Statementlist OUT OptNL } ${ $0 = $<Sl; }$
3014 | { SimpleStatements } ${ $0 = reorder_bilist($<SS); }$
3015 | : SimpleStatements ; ${ $0 = reorder_bilist($<SS); }$
3016 | : SimpleStatements EOL ${ $0 = reorder_bilist($<SS); }$
3017 | : IN OptNL Statementlist OUT ${ $0 = $<Sl; }$
3019 Statementlist -> ComplexStatements ${ $0 = reorder_bilist($<CS); }$
3021 ComplexStatements -> ComplexStatements ComplexStatement ${
3031 | ComplexStatement ${
3043 ComplexStatement -> SimpleStatements Newlines ${
3044 $0 = reorder_bilist($<SS);
3046 | SimpleStatements ; Newlines ${
3047 $0 = reorder_bilist($<SS);
3049 ## ComplexStatement Grammar
3052 SimpleStatements -> SimpleStatements ; SimpleStatement ${
3058 | SimpleStatement ${
3066 SimpleStatement -> pass ${ $0 = NULL; }$
3067 | ERROR ${ tok_err(c, "Syntax error in statement", &$1); }$
3068 ## SimpleStatement Grammar
3070 ###### print binode cases
3074 if (b->left == NULL)
3077 print_exec(b->left, indent, bracket);
3080 print_exec(b->right, indent, bracket);
3083 // block, one per line
3084 if (b->left == NULL)
3085 do_indent(indent, "pass\n");
3087 print_exec(b->left, indent, bracket);
3089 print_exec(b->right, indent, bracket);
3093 ###### propagate binode cases
3096 /* If any statement returns something other than Tnone
3097 * or Tbool then all such must return same type.
3098 * As each statement may be Tnone or something else,
3099 * we must always pass NULL (unknown) down, otherwise an incorrect
3100 * error might occur. We never return Tnone unless it is
3105 for (e = b; e; e = cast(binode, e->right)) {
3106 t = propagate_types(e->left, c, ok, NULL, rules);
3107 if ((rules & Rboolok) && t == Tbool)
3109 if (t && t != Tnone && t != Tbool) {
3113 type_err(c, "error: expected %1%r, found %2",
3114 e->left, type, rules, t);
3120 ###### interp binode cases
3122 while (rvtype == Tnone &&
3125 rv = interp_exec(b->left, &rvtype);
3126 b = cast(binode, b->right);
3130 ### The Print statement
3132 `print` is a simple statement that takes a comma-separated list of
3133 expressions and prints the values separated by spaces and terminated
3134 by a newline. No control of formatting is possible.
3136 `print` faces the same list-ordering issue as blocks, and uses the
3142 ##### expr precedence
3145 ###### SimpleStatement Grammar
3147 | print ExpressionList ${
3148 $0 = reorder_bilist($<2);
3150 | print ExpressionList , ${
3155 $0 = reorder_bilist($0);
3166 ExpressionList -> ExpressionList , Expression ${
3179 ###### print binode cases
3182 do_indent(indent, "print");
3186 print_exec(b->left, -1, bracket);
3190 b = cast(binode, b->right);
3196 ###### propagate binode cases
3199 /* don't care but all must be consistent */
3200 propagate_types(b->left, c, ok, NULL, Rnolabel);
3201 propagate_types(b->right, c, ok, NULL, Rnolabel);
3204 ###### interp binode cases
3210 for ( ; b; b = cast(binode, b->right))
3214 left = interp_exec(b->left, <ype);
3215 print_value(ltype, &left);
3216 free_value(ltype, &left);
3227 ###### Assignment statement
3229 An assignment will assign a value to a variable, providing it hasn't
3230 been declared as a constant. The analysis phase ensures that the type
3231 will be correct so the interpreter just needs to perform the
3232 calculation. There is a form of assignment which declares a new
3233 variable as well as assigning a value. If a name is assigned before
3234 it is declared, and error will be raised as the name is created as
3235 `Tlabel` and it is illegal to assign to such names.
3241 ###### declare terminals
3244 ###### SimpleStatement Grammar
3245 | Variable = Expression ${
3251 | VariableDecl = Expression ${
3259 if ($1->var->where_set == NULL) {
3261 "Variable declared with no type or value: %v",
3271 ###### print binode cases
3274 do_indent(indent, "");
3275 print_exec(b->left, indent, bracket);
3277 print_exec(b->right, indent, bracket);
3284 struct variable *v = cast(var, b->left)->var;
3285 do_indent(indent, "");
3286 print_exec(b->left, indent, bracket);
3287 if (cast(var, b->left)->var->constant) {
3288 if (v->where_decl == v->where_set) {
3290 type_print(v->type, stdout);
3295 if (v->where_decl == v->where_set) {
3297 type_print(v->type, stdout);
3304 print_exec(b->right, indent, bracket);
3311 ###### propagate binode cases
3315 /* Both must match and not be labels,
3316 * Type must support 'dup',
3317 * For Assign, left must not be constant.
3320 t = propagate_types(b->left, c, ok, NULL,
3321 Rnolabel | (b->op == Assign ? Rnoconstant : 0));
3326 if (propagate_types(b->right, c, ok, t, 0) != t)
3327 if (b->left->type == Xvar)
3328 type_err(c, "info: variable '%v' was set as %1 here.",
3329 cast(var, b->left)->var->where_set, t, rules, NULL);
3331 t = propagate_types(b->right, c, ok, NULL, Rnolabel);
3333 propagate_types(b->left, c, ok, t,
3334 (b->op == Assign ? Rnoconstant : 0));
3336 if (t && t->dup == NULL)
3337 type_err(c, "error: cannot assign value of type %1", b, t, 0, NULL);
3342 ###### interp binode cases
3345 lleft = linterp_exec(b->left, <ype);
3346 right = interp_exec(b->right, &rtype);
3348 free_value(ltype, lleft);
3349 dup_value(ltype, &right, lleft);
3356 struct variable *v = cast(var, b->left)->var;
3360 right = interp_exec(b->right, &rtype);
3361 free_value(v->type, v->val);
3363 v->val = val_alloc(v->type, &right);
3366 free_value(v->type, v->val);
3368 v->val = val_alloc(v->type, NULL);
3373 ### The `use` statement
3375 The `use` statement is the last "simple" statement. It is needed when
3376 the condition in a conditional statement is a block. `use` works much
3377 like `return` in C, but only completes the `condition`, not the whole
3383 ###### expr precedence
3386 ###### SimpleStatement Grammar
3388 $0 = new_pos(binode, $1);
3391 if ($0->right->type == Xvar) {
3392 struct var *v = cast(var, $0->right);
3393 if (v->var->type == Tnone) {
3394 /* Convert this to a label */
3395 v->var->type = Tlabel;
3396 v->var->val = val_alloc(Tlabel, NULL);
3397 v->var->val->label = v->var->val;
3402 ###### print binode cases
3405 do_indent(indent, "use ");
3406 print_exec(b->right, -1, bracket);
3411 ###### propagate binode cases
3414 /* result matches value */
3415 return propagate_types(b->right, c, ok, type, 0);
3417 ###### interp binode cases
3420 rv = interp_exec(b->right, &rvtype);
3423 ### The Conditional Statement
3425 This is the biggy and currently the only complex statement. This
3426 subsumes `if`, `while`, `do/while`, `switch`, and some parts of `for`.
3427 It is comprised of a number of parts, all of which are optional though
3428 set combinations apply. Each part is (usually) a key word (`then` is
3429 sometimes optional) followed by either an expression or a code block,
3430 except the `casepart` which is a "key word and an expression" followed
3431 by a code block. The code-block option is valid for all parts and,
3432 where an expression is also allowed, the code block can use the `use`
3433 statement to report a value. If the code block does not report a value
3434 the effect is similar to reporting `True`.
3436 The `else` and `case` parts, as well as `then` when combined with
3437 `if`, can contain a `use` statement which will apply to some
3438 containing conditional statement. `for` parts, `do` parts and `then`
3439 parts used with `for` can never contain a `use`, except in some
3440 subordinate conditional statement.
3442 If there is a `forpart`, it is executed first, only once.
3443 If there is a `dopart`, then it is executed repeatedly providing
3444 always that the `condpart` or `cond`, if present, does not return a non-True
3445 value. `condpart` can fail to return any value if it simply executes
3446 to completion. This is treated the same as returning `True`.
3448 If there is a `thenpart` it will be executed whenever the `condpart`
3449 or `cond` returns True (or does not return any value), but this will happen
3450 *after* `dopart` (when present).
3452 If `elsepart` is present it will be executed at most once when the
3453 condition returns `False` or some value that isn't `True` and isn't
3454 matched by any `casepart`. If there are any `casepart`s, they will be
3455 executed when the condition returns a matching value.
3457 The particular sorts of values allowed in case parts has not yet been
3458 determined in the language design, so nothing is prohibited.
3460 The various blocks in this complex statement potentially provide scope
3461 for variables as described earlier. Each such block must include the
3462 "OpenScope" nonterminal before parsing the block, and must call
3463 `var_block_close()` when closing the block.
3465 The code following "`if`", "`switch`" and "`for`" does not get its own
3466 scope, but is in a scope covering the whole statement, so names
3467 declared there cannot be redeclared elsewhere. Similarly the
3468 condition following "`while`" is in a scope the covers the body
3469 ("`do`" part) of the loop, and which does not allow conditional scope
3470 extension. Code following "`then`" (both looping and non-looping),
3471 "`else`" and "`case`" each get their own local scope.
3473 The type requirements on the code block in a `whilepart` are quite
3474 unusal. It is allowed to return a value of some identifiable type, in
3475 which case the loop aborts and an appropriate `casepart` is run, or it
3476 can return a Boolean, in which case the loop either continues to the
3477 `dopart` (on `True`) or aborts and runs the `elsepart` (on `False`).
3478 This is different both from the `ifpart` code block which is expected to
3479 return a Boolean, or the `switchpart` code block which is expected to
3480 return the same type as the casepart values. The correct analysis of
3481 the type of the `whilepart` code block is the reason for the
3482 `Rboolok` flag which is passed to `propagate_types()`.
3484 The `cond_statement` cannot fit into a `binode` so a new `exec` is
3493 struct exec *action;
3494 struct casepart *next;
3496 struct cond_statement {
3498 struct exec *forpart, *condpart, *dopart, *thenpart, *elsepart;
3499 struct casepart *casepart;
3502 ###### ast functions
3504 static void free_casepart(struct casepart *cp)
3508 free_exec(cp->value);
3509 free_exec(cp->action);
3516 static void free_cond_statement(struct cond_statement *s)
3520 free_exec(s->forpart);
3521 free_exec(s->condpart);
3522 free_exec(s->dopart);
3523 free_exec(s->thenpart);
3524 free_exec(s->elsepart);
3525 free_casepart(s->casepart);
3529 ###### free exec cases
3530 case Xcond_statement: free_cond_statement(cast(cond_statement, e)); break;
3532 ###### ComplexStatement Grammar
3533 | CondStatement ${ $0 = $<1; }$
3535 ###### expr precedence
3536 $TERM for then while do
3543 // A CondStatement must end with EOL, as does CondSuffix and
3545 // ForPart, ThenPart, SwitchPart, CasePart are non-empty and
3546 // may or may not end with EOL
3547 // WhilePart and IfPart include an appropriate Suffix
3550 // Both ForPart and Whilepart open scopes, and CondSuffix only
3551 // closes one - so in the first branch here we have another to close.
3552 CondStatement -> ForPart OptNL ThenPart OptNL WhilePart CondSuffix ${
3555 $0->thenpart = $<TP;
3556 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3557 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3558 var_block_close(c, CloseSequential);
3560 | ForPart OptNL WhilePart CondSuffix ${
3563 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3564 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3565 var_block_close(c, CloseSequential);
3567 | WhilePart CondSuffix ${
3569 $0->condpart = $WP.condpart; $WP.condpart = NULL;
3570 $0->dopart = $WP.dopart; $WP.dopart = NULL;
3572 | SwitchPart OptNL CasePart CondSuffix ${
3574 $0->condpart = $<SP;
3575 $CP->next = $0->casepart;
3576 $0->casepart = $<CP;
3578 | SwitchPart : IN OptNL CasePart CondSuffix OUT Newlines ${
3580 $0->condpart = $<SP;
3581 $CP->next = $0->casepart;
3582 $0->casepart = $<CP;
3584 | IfPart IfSuffix ${
3586 $0->condpart = $IP.condpart; $IP.condpart = NULL;
3587 $0->thenpart = $IP.thenpart; $IP.thenpart = NULL;
3588 // This is where we close an "if" statement
3589 var_block_close(c, CloseSequential);
3592 CondSuffix -> IfSuffix ${
3594 // This is where we close scope of the whole
3595 // "for" or "while" statement
3596 var_block_close(c, CloseSequential);
3598 | Newlines CasePart CondSuffix ${
3600 $CP->next = $0->casepart;
3601 $0->casepart = $<CP;
3603 | CasePart CondSuffix ${
3605 $CP->next = $0->casepart;
3606 $0->casepart = $<CP;
3609 IfSuffix -> Newlines ${ $0 = new(cond_statement); }$
3610 | Newlines ElsePart ${ $0 = $<EP; }$
3611 | ElsePart ${$0 = $<EP; }$
3613 ElsePart -> else OpenBlock Newlines ${
3614 $0 = new(cond_statement);
3615 $0->elsepart = $<OB;
3616 var_block_close(c, CloseElse);
3618 | else OpenScope CondStatement ${
3619 $0 = new(cond_statement);
3620 $0->elsepart = $<CS;
3621 var_block_close(c, CloseElse);
3625 CasePart -> case Expression OpenScope ColonBlock ${
3626 $0 = calloc(1,sizeof(struct casepart));
3629 var_block_close(c, CloseParallel);
3633 // These scopes are closed in CondSuffix
3634 ForPart -> for OpenBlock ${
3638 ThenPart -> then OpenBlock ${
3640 var_block_close(c, CloseSequential);
3644 // This scope is closed in CondSuffix
3645 WhilePart -> while UseBlock OptNL do Block ${
3649 | while OpenScope Expression ColonBlock ${
3650 $0.condpart = $<Exp;
3654 IfPart -> if UseBlock OptNL then OpenBlock ClosePara ${
3658 | if OpenScope Expression OpenScope ColonBlock ClosePara ${
3662 | if OpenScope Expression OpenScope OptNL then Block ClosePara ${
3668 // This scope is closed in CondSuffix
3669 SwitchPart -> switch OpenScope Expression ${
3672 | switch UseBlock ${
3676 ###### print exec cases
3678 case Xcond_statement:
3680 struct cond_statement *cs = cast(cond_statement, e);
3681 struct casepart *cp;
3683 do_indent(indent, "for");
3684 if (bracket) printf(" {\n"); else printf("\n");
3685 print_exec(cs->forpart, indent+1, bracket);
3688 do_indent(indent, "} then {\n");
3690 do_indent(indent, "then\n");
3691 print_exec(cs->thenpart, indent+1, bracket);
3693 if (bracket) do_indent(indent, "}\n");
3697 if (cs->condpart && cs->condpart->type == Xbinode &&
3698 cast(binode, cs->condpart)->op == Block) {
3700 do_indent(indent, "while {\n");
3702 do_indent(indent, "while\n");
3703 print_exec(cs->condpart, indent+1, bracket);
3705 do_indent(indent, "} do {\n");
3707 do_indent(indent, "do\n");
3708 print_exec(cs->dopart, indent+1, bracket);
3710 do_indent(indent, "}\n");
3712 do_indent(indent, "while ");
3713 print_exec(cs->condpart, 0, bracket);
3718 print_exec(cs->dopart, indent+1, bracket);
3720 do_indent(indent, "}\n");
3725 do_indent(indent, "switch");
3727 do_indent(indent, "if");
3728 if (cs->condpart && cs->condpart->type == Xbinode &&
3729 cast(binode, cs->condpart)->op == Block) {
3734 print_exec(cs->condpart, indent+1, bracket);
3736 do_indent(indent, "}\n");
3738 do_indent(indent, "then:\n");
3739 print_exec(cs->thenpart, indent+1, bracket);
3743 print_exec(cs->condpart, 0, bracket);
3749 print_exec(cs->thenpart, indent+1, bracket);
3751 do_indent(indent, "}\n");
3756 for (cp = cs->casepart; cp; cp = cp->next) {
3757 do_indent(indent, "case ");
3758 print_exec(cp->value, -1, 0);
3763 print_exec(cp->action, indent+1, bracket);
3765 do_indent(indent, "}\n");
3768 do_indent(indent, "else");
3773 print_exec(cs->elsepart, indent+1, bracket);
3775 do_indent(indent, "}\n");
3780 ###### propagate exec cases
3781 case Xcond_statement:
3783 // forpart and dopart must return Tnone
3784 // thenpart must return Tnone if there is a dopart,
3785 // otherwise it is like elsepart.
3787 // be bool if there is no casepart
3788 // match casepart->values if there is a switchpart
3789 // either be bool or match casepart->value if there
3791 // elsepart and casepart->action must match the return type
3792 // expected of this statement.
3793 struct cond_statement *cs = cast(cond_statement, prog);
3794 struct casepart *cp;
3796 t = propagate_types(cs->forpart, c, ok, Tnone, 0);
3797 if (!type_compat(Tnone, t, 0))
3799 t = propagate_types(cs->dopart, c, ok, Tnone, 0);
3800 if (!type_compat(Tnone, t, 0))
3803 t = propagate_types(cs->thenpart, c, ok, Tnone, 0);
3804 if (!type_compat(Tnone, t, 0))
3807 if (cs->casepart == NULL)
3808 propagate_types(cs->condpart, c, ok, Tbool, 0);
3810 /* Condpart must match case values, with bool permitted */
3812 for (cp = cs->casepart;
3813 cp && !t; cp = cp->next)
3814 t = propagate_types(cp->value, c, ok, NULL, 0);
3815 if (!t && cs->condpart)
3816 t = propagate_types(cs->condpart, c, ok, NULL, Rboolok);
3817 // Now we have a type (I hope) push it down
3819 for (cp = cs->casepart; cp; cp = cp->next)
3820 propagate_types(cp->value, c, ok, t, 0);
3821 propagate_types(cs->condpart, c, ok, t, Rboolok);
3824 // (if)then, else, and case parts must return expected type.
3825 if (!cs->dopart && !type)
3826 type = propagate_types(cs->thenpart, c, ok, NULL, rules);
3828 type = propagate_types(cs->elsepart, c, ok, NULL, rules);
3829 for (cp = cs->casepart;
3832 type = propagate_types(cp->action, c, ok, NULL, rules);
3835 propagate_types(cs->thenpart, c, ok, type, rules);
3836 propagate_types(cs->elsepart, c, ok, type, rules);
3837 for (cp = cs->casepart; cp ; cp = cp->next)
3838 propagate_types(cp->action, c, ok, type, rules);
3844 ###### interp exec cases
3845 case Xcond_statement:
3847 struct value v, cnd;
3848 struct type *vtype, *cndtype;
3849 struct casepart *cp;
3850 struct cond_statement *c = cast(cond_statement, e);
3853 interp_exec(c->forpart, NULL);
3856 cnd = interp_exec(c->condpart, &cndtype);
3859 if (!(cndtype == Tnone ||
3860 (cndtype == Tbool && cnd.bool != 0)))
3862 // cnd is Tnone or Tbool, doesn't need to be freed
3864 interp_exec(c->dopart, NULL);
3867 rv = interp_exec(c->thenpart, &rvtype);
3868 if (rvtype != Tnone || !c->dopart)
3870 free_value(rvtype, &rv);
3873 } while (c->dopart);
3875 for (cp = c->casepart; cp; cp = cp->next) {
3876 v = interp_exec(cp->value, &vtype);
3877 if (value_cmp(cndtype, vtype, &v, &cnd) == 0) {
3878 free_value(vtype, &v);
3879 free_value(cndtype, &cnd);
3880 rv = interp_exec(cp->action, &rvtype);
3883 free_value(vtype, &v);
3885 free_value(cndtype, &cnd);
3887 rv = interp_exec(c->elsepart, &rvtype);
3894 ### Top level structure
3896 All the language elements so far can be used in various places. Now
3897 it is time to clarify what those places are.
3899 At the top level of a file there will be a number of declarations.
3900 Many of the things that can be declared haven't been described yet,
3901 such as functions, procedures, imports, and probably more.
3902 For now there are two sorts of things that can appear at the top
3903 level. They are predefined constants, `struct` types, and the main
3904 program. While the syntax will allow the main program to appear
3905 multiple times, that will trigger an error if it is actually attempted.
3907 The various declarations do not return anything. They store the
3908 various declarations in the parse context.
3910 ###### Parser: grammar
3913 Ocean -> OptNL DeclarationList
3915 ## declare terminals
3922 DeclarationList -> Declaration
3923 | DeclarationList Declaration
3925 Declaration -> ERROR Newlines ${
3927 "error: unhandled parse error", &$1);
3933 ## top level grammar
3935 ### The `const` section
3937 As well as being defined in with the code that uses them, constants
3938 can be declared at the top level. These have full-file scope, so they
3939 are always `InScope`. The value of a top level constant can be given
3940 as an expression, and this is evaluated immediately rather than in the
3941 later interpretation stage. Once we add functions to the language, we
3942 will need rules concern which, if any, can be used to define a top
3945 Constants are defined in a section that starts with the reserved word
3946 `const` and then has a block with a list of assignment statements.
3947 For syntactic consistency, these must use the double-colon syntax to
3948 make it clear that they are constants. Type can also be given: if
3949 not, the type will be determined during analysis, as with other
3952 As the types constants are inserted at the head of a list, printing
3953 them in the same order that they were read is not straight forward.
3954 We take a quadratic approach here and count the number of constants
3955 (variables of depth 0), then count down from there, each time
3956 searching through for the Nth constant for decreasing N.
3958 ###### top level grammar
3962 DeclareConstant -> const { IN OptNL ConstList OUT OptNL } Newlines
3963 | const { SimpleConstList } Newlines
3964 | const IN OptNL ConstList OUT Newlines
3965 | const SimpleConstList Newlines
3967 ConstList -> ConstList SimpleConstLine
3969 SimpleConstList -> SimpleConstList ; Const
3972 SimpleConstLine -> SimpleConstList Newlines
3973 | ERROR Newlines ${ tok_err(c, "Syntax error in constant", &$1); }$
3976 CType -> Type ${ $0 = $<1; }$
3979 Const -> IDENTIFIER :: CType = Expression ${ {
3983 v = var_decl(c, $1.txt);
3985 struct var *var = new_pos(var, $1);
3986 v->where_decl = var;
3991 v = var_ref(c, $1.txt);
3992 tok_err(c, "error: name already declared", &$1);
3993 type_err(c, "info: this is where '%v' was first declared",
3994 v->where_decl, NULL, 0, NULL);
3998 propagate_types($5, c, &ok, $3, 0);
4003 struct value res = interp_exec($5, &v->type);
4004 v->val = val_alloc(v->type, &res);
4008 ###### print const decls
4013 while (target != 0) {
4015 for (v = context.in_scope; v; v=v->in_scope)
4016 if (v->depth == 0) {
4027 printf(" %.*s :: ", v->name->name.len, v->name->name.txt);
4028 type_print(v->type, stdout);
4030 if (v->type == Tstr)
4032 print_value(v->type, v->val);
4033 if (v->type == Tstr)
4041 ### Finally the whole program.
4043 Somewhat reminiscent of Pascal a (current) Ocean program starts with
4044 the keyword "program" and a list of variable names which are assigned
4045 values from command line arguments. Following this is a `block` which
4046 is the code to execute. Unlike Pascal, constants and other
4047 declarations come *before* the program.
4049 As this is the top level, several things are handled a bit
4051 The whole program is not interpreted by `interp_exec` as that isn't
4052 passed the argument list which the program requires. Similarly type
4053 analysis is a bit more interesting at this level.
4058 ###### top level grammar
4060 DeclareProgram -> Program ${ {
4062 type_err(c, "Program defined a second time",
4071 Program -> program OpenScope Varlist ColonBlock Newlines ${
4074 $0->left = reorder_bilist($<Vl);
4076 var_block_close(c, CloseSequential);
4077 if (c->scope_stack && !c->parse_error) abort();
4080 Varlist -> Varlist ArgDecl ${
4089 ArgDecl -> IDENTIFIER ${ {
4090 struct variable *v = var_decl(c, $1.txt);
4097 ###### print binode cases
4099 do_indent(indent, "program");
4100 for (b2 = cast(binode, b->left); b2; b2 = cast(binode, b2->right)) {
4102 print_exec(b2->left, 0, 0);
4108 print_exec(b->right, indent+1, bracket);
4110 do_indent(indent, "}\n");
4113 ###### propagate binode cases
4114 case Program: abort(); // NOTEST
4116 ###### core functions
4118 static int analyse_prog(struct exec *prog, struct parse_context *c)
4120 struct binode *b = cast(binode, prog);
4127 propagate_types(b->right, c, &ok, Tnone, 0);
4132 for (b = cast(binode, b->left); b; b = cast(binode, b->right)) {
4133 struct var *v = cast(var, b->left);
4134 if (!v->var->type) {
4135 v->var->where_set = b;
4136 v->var->type = Tstr;
4140 b = cast(binode, prog);
4143 propagate_types(b->right, c, &ok, Tnone, 0);
4148 /* Make sure everything is still consistent */
4149 propagate_types(b->right, c, &ok, Tnone, 0);
4153 static void interp_prog(struct exec *prog, char **argv)
4155 struct binode *p = cast(binode, prog);
4162 al = cast(binode, p->left);
4164 struct var *v = cast(var, al->left);
4165 struct value *vl = v->var->val;
4167 if (argv[0] == NULL) {
4168 printf("Not enough args\n");
4171 al = cast(binode, al->right);
4173 free_value(v->var->type, vl);
4175 vl = val_alloc(v->var->type, NULL);
4178 free_value(v->var->type, vl);
4179 vl->str.len = strlen(argv[0]);
4180 vl->str.txt = malloc(vl->str.len);
4181 memcpy(vl->str.txt, argv[0], vl->str.len);
4184 v = interp_exec(p->right, &vtype);
4185 free_value(vtype, &v);
4188 ###### interp binode cases
4189 case Program: abort(); // NOTEST
4191 ## And now to test it out.
4193 Having a language requires having a "hello world" program. I'll
4194 provide a little more than that: a program that prints "Hello world"
4195 finds the GCD of two numbers, prints the first few elements of
4196 Fibonacci, performs a binary search for a number, and a few other
4197 things which will likely grow as the languages grows.
4199 ###### File: oceani.mk
4202 @echo "===== DEMO ====="
4203 ./oceani --section "demo: hello" oceani.mdc 55 33
4209 four ::= 2 + 2 ; five ::= 10/2
4210 const pie ::= "I like Pie";
4211 cake ::= "The cake is"
4220 print "Hello World, what lovely oceans you have!"
4221 print "Are there", five, "?"
4222 print pi, pie, "but", cake
4224 A := $Astr; B := $Bstr
4226 /* When a variable is defined in both branches of an 'if',
4227 * and used afterwards, the variables are merged.
4233 print "Is", A, "bigger than", B,"? ", bigger
4234 /* If a variable is not used after the 'if', no
4235 * merge happens, so types can be different
4238 double:string = "yes"
4239 print A, "is more than twice", B, "?", double
4242 print "double", B, "is", double
4247 if a > 0 and then b > 0:
4253 print "GCD of", A, "and", B,"is", a
4255 print a, "is not positive, cannot calculate GCD"
4257 print b, "is not positive, cannot calculate GCD"
4262 print "Fibonacci:", f1,f2,
4263 then togo = togo - 1
4271 /* Binary search... */
4276 mid := (lo + hi) / 2
4288 print "Yay, I found", target
4290 print "Closest I found was", mid
4295 // "middle square" PRNG. Not particularly good, but one my
4296 // Dad taught me - the first one I ever heard of.
4297 for i:=1; then i = i + 1; while i < size:
4298 n := list[i-1] * list[i-1]
4299 list[i] = (n / 100) % 10 000
4301 print "Before sort:",
4302 for i:=0; then i = i + 1; while i < size:
4306 for i := 1; then i=i+1; while i < size:
4307 for j:=i-1; then j=j-1; while j >= 0:
4308 if list[j] > list[j+1]:
4312 print " After sort:",
4313 for i:=0; then i = i + 1; while i < size:
4317 if 1 == 2 then print "yes"; else print "no"
4321 bob.alive = (bob.name == "Hello")
4322 print "bob", "is" if bob.alive else "isn't", "alive"