1 # LR(1) Parser Generator #
3 This parser generator takes a grammar description combined with code
4 fragments, analyses it, and can report details about the analysis and
5 write out C code files which can be compiled to make a parser.
7 There are several distinct sections.
9 1. `grammar_read` will read a grammar from a literate-code file and
10 store the productions, symbols, and code fragments.
11 2. `grammar_analyse` will take that grammar and build LR parsing
12 states and look-ahead tables.
13 3. `grammar_report` will present the details of the analysis
14 in a readable format and will report any conflicts.
15 4. `parser_generate` will write out C code files with various
16 tables and with the code fragments arranged in useful places.
17 5. `parser_run` is a library function intended to be linked together
18 with the generated parser tables to complete the implementation of
20 6. Finally `calc` is a test grammar for a simple calculator. The
21 `parsergen` program built from the C code in this file can extract
22 that grammar directly from this file and process it.
25 ###### File: parsergen.c
30 ## forward declarations
41 ###### File: libparser.c
48 ###### File: parsergen.mk
51 parsergen.c parsergen.mk libparser.c parser.h : parsergen.mdc
54 ## Reading the grammar
56 The grammar must be stored in a markdown literate code file as parsed
57 by "[mdcode][]". It must have three top level (i.e. unreferenced)
58 sections: `header`, `code`, and `grammar`. The first two will be
59 literally copied into the generated `.c` and `.h`. files. The last
60 contains the grammar. This is tokenised with "[scanner][]".
62 If the `--tag` option is given, then any top level header that doesn't
63 start with the tag is ignored, and the tag is striped from the rest. So
65 means that the three needed sections must be `Foo: header`, `Foo: code`,
69 [scanner]: scanner.html
75 ###### parser includes
79 The grammar contains production sets, precedence/associativity
80 declarations, and data type declarations. These are all parsed with
81 _ad hoc_ parsing as we don't have a parser generator yet.
83 The precedence and associativity can be set for each production, but
84 can be inherited from symbols. The data type (either structure or a
85 reference to a structure) is potentially defined for each non-terminal
86 and describes what C structure is used to store information about each
90 enum assoc {Left, Right, Non};
91 char *assoc_names[] = {"Left","Right","Non"};
94 struct text struct_name;
97 unsigned short precedence;
101 unsigned short precedence;
109 The strings reported by `mdcode` and `scanner` are `struct text` which have
110 length rather than being null terminated. To help with printing and
111 comparing we define `text_is` and `prtxt`, which should possibly go in
112 `mdcode`. `scanner` does provide `text_dump` which is useful for strings
113 which might contain control characters.
115 `strip_tag` is a bit like `strncmp`, but adds a test for a colon,
116 because that is what we need to detect tags.
119 static int text_is(struct text t, char *s)
121 return (strlen(s) == t.len &&
122 strncmp(s, t.txt, t.len) == 0);
124 static void prtxt(struct text t)
126 printf("%.*s", t.len, t.txt);
129 static int strip_tag(struct text *t, char *tag)
131 int skip = strlen(tag) + 1;
132 if (skip >= t->len ||
133 strncmp(t->txt, tag, skip-1) != 0 ||
134 t->txt[skip-1] != ':')
136 while (skip < t->len && t->txt[skip] == ' ')
145 Productions are comprised primarily of symbols - terminal and
146 non-terminal. We do not make a syntactic distinction between the two,
147 though non-terminals must be identifiers. Non-terminal symbols are
148 those which appear in the head of a production, terminal symbols are
149 those which don't. There are also "virtual" symbols used for precedence
150 marking discussed later, and sometimes we won't know what type a symbol
153 ###### forward declarations
154 enum symtype { Unknown, Virtual, Terminal, Nonterminal };
155 char *symtypes = "UVTN";
159 Symbols can be either `TK_ident` or `TK_mark`. They are saved in a
160 table of known symbols and the resulting parser will report them as
161 `TK_reserved + N`. A small set of identifiers are reserved for the
162 different token types that `scanner` can report.
165 static char *reserved_words[] = {
166 [TK_error] = "ERROR",
167 [TK_number] = "NUMBER",
168 [TK_ident] = "IDENTIFIER",
170 [TK_string] = "STRING",
171 [TK_multi_string] = "MULTI_STRING",
174 [TK_newline] = "NEWLINE",
180 Note that `TK_eof` and the two `TK_*_comment` tokens cannot be
181 recognised. The former is automatically expected at the end of the text
182 being parsed. The latter are always ignored by the parser.
184 All of these symbols are stored in a simple symbol table. We use the
185 `struct text` from `mdcode` to store the name and link them together
186 into a sorted list using an insertion sort.
188 We don't have separate `find` and `insert` functions as any symbol we
189 find needs to be remembered. We simply expect `find` to always return a
190 symbol, but its type might be `Unknown`.
199 ###### grammar fields
204 static struct symbol *sym_find(struct grammar *g, struct text s)
206 struct symbol **l = &g->syms;
211 (cmp = text_cmp((*l)->name, s)) < 0)
215 n = calloc(1, sizeof(*n));
224 static void symbols_init(struct grammar *g)
226 int entries = sizeof(reserved_words)/sizeof(reserved_words[0]);
228 for (i = 0; i < entries; i++) {
231 t.txt = reserved_words[i];
234 t.len = strlen(t.txt);
241 ### Data types and precedence.
243 Data type specification and precedence specification are both
244 introduced by a dollar sign at the start of the line. If the next
245 word is `LEFT`, `RIGHT` or `NON`, then the line specifies a
246 precedence, otherwise it specifies a data type.
248 The data type name is simply stored and applied to the head of all
249 subsequent productions. It must be the name of a structure optionally
250 preceded by an asterisk which means a reference or "pointer". So
251 `$expression` maps to `struct expression` and `$*statement` maps to
252 `struct statement *`.
254 Any productions given before the first data type declaration will have
255 no data type associated with them and can carry no information. In
256 order to allow other non-terminals to have no type, the data type
257 `$void` can be given. This does *not* mean that `struct void` will be
258 used, but rather than no type will be associated with future
261 The precedence line must contain a list of symbols - typically
262 terminal symbols, but not necessarily. It can only contain symbols
263 that have not been seen yet, so precedence declaration must precede
264 the productions that they affect.
266 A precedence line may also contain a "virtual" symbol which is an
267 identifier preceded by `$$`. Virtual terminals carry precedence
268 information but are not included in the grammar. A production can
269 declare that it inherits the precedence of a given virtual symbol.
271 This use for `$$` precludes it from being used as a symbol in the
272 described language. Two other symbols: `${` and `}$` are also
275 Each new precedence line introduces a new precedence level and
276 declares how it associates. This level is stored in each symbol
277 listed and may be inherited by any production which uses the symbol. A
278 production inherits from the last symbol which has a precedence.
280 ###### grammar fields
281 struct text current_type;
286 enum symbols { TK_virtual = TK_reserved, TK_open, TK_close };
287 static const char *known[] = { "$$", "${", "}$" };
290 static char *dollar_line(struct token_state *ts, struct grammar *g, int isref)
292 struct token t = token_next(ts);
297 if (t.num != TK_ident) {
298 err = "type or assoc expected after '$'";
301 if (text_is(t.txt, "LEFT"))
303 else if (text_is(t.txt, "RIGHT"))
305 else if (text_is(t.txt, "NON"))
308 g->current_type = t.txt;
309 g->type_isref = isref;
310 if (text_is(t.txt, "void"))
311 g->current_type.txt = NULL;
313 if (t.num != TK_newline) {
314 err = "Extra tokens after type name";
321 err = "$* cannot be followed by a precedence";
325 // This is a precedence line, need some symbols.
329 while (t.num != TK_newline) {
330 enum symtype type = Terminal;
332 if (t.num == TK_virtual) {
335 if (t.num != TK_ident) {
336 err = "$$ must be followed by a word";
339 } else if (t.num != TK_ident &&
341 err = "Illegal token in precedence line";
344 s = sym_find(g, t.txt);
345 if (s->type != Unknown) {
346 err = "Symbols in precedence line must not already be known.";
350 s->precedence = g->prec_levels;
355 err = "No symbols given on precedence line";
359 while (t.num != TK_newline && t.num != TK_eof)
366 A production either starts with an identifier which is the head
367 non-terminal, or a vertical bar (`|`) in which case this production
368 uses the same head as the previous one. The identifier must be
369 followed by a `->` mark. All productions for a given non-terminal must
370 be grouped together with the `nonterminal ->` given only once.
372 After this a (possibly empty) sequence of identifiers and marks form
373 the body of the production. A virtual symbol may be given after the
374 body by preceding it with `$$`. If a virtual symbol is given, the
375 precedence of the production is that for the virtual symbol. If none
376 is given, the precedence is inherited from the last symbol in the
377 production which has a precedence specified.
379 After the optional precedence may come the `${` mark. This indicates
380 the start of a code fragment. If present, this must be on the same
381 line as the start of the production.
383 All of the text from the `${` through to the matching `}$` is
384 collected and forms the code-fragment for the production. It must all
385 be in one `code_node` of the literate code. The `}$` must be
386 at the end of a line.
388 Text in the code fragment will undergo substitutions where `$N` or
389 `$<N`,for some numeric `N`, will be replaced with a variable holding
390 the parse information for the particular symbol in the production.
391 `$0` is the head of the production, `$1` is the first symbol of the
392 body, etc. The type of `$N` for a terminal symbol is `struct token`.
393 For a non-terminal, it is whatever has been declared for that symbol.
394 The `<` may be included for symbols declared as storing a reference
395 (not a structure) and means that the reference is being moved out, so
396 it will not automatically be freed.
398 While building productions we will need to add to an array which needs to
402 static void array_add(void *varray, int *cnt, void *new)
404 void ***array = varray;
407 current = ((*cnt-1) | (step-1))+1;
408 if (*cnt == current) {
411 *array = realloc(*array, current * sizeof(void*));
413 (*array)[*cnt] = new;
417 Collecting the code fragment simply involves reading tokens until we
418 hit the end token `}$`, and noting the character position of the start and
422 static struct text collect_code(struct token_state *state,
427 code.txt = start.txt.txt + start.txt.len;
429 t = token_next(state);
430 while (t.node == start.node &&
431 t.num != TK_close && t.num != TK_error &&
433 if (t.num == TK_close && t.node == start.node)
434 code.len = t.txt.txt - code.txt;
440 Now we have all the bit we need to parse a full production.
445 ###### grammar fields
446 struct production **productions;
447 int production_count;
449 ###### production fields
451 struct symbol **body;
456 int first_production;
459 static char *parse_production(struct grammar *g,
461 struct token_state *state)
463 /* Head has already been parsed. */
466 struct production p, *pp;
468 memset(&p, 0, sizeof(p));
470 tk = token_next(state);
471 while (tk.num == TK_ident || tk.num == TK_mark) {
472 struct symbol *bs = sym_find(g, tk.txt);
473 if (bs->type == Unknown)
475 if (bs->type == Virtual) {
476 err = "Virtual symbol not permitted in production";
479 if (bs->precedence) {
480 p.precedence = bs->precedence;
483 array_add(&p.body, &p.body_size, bs);
484 tk = token_next(state);
486 if (tk.num == TK_virtual) {
488 tk = token_next(state);
489 if (tk.num != TK_ident) {
490 err = "word required after $$";
493 vs = sym_find(g, tk.txt);
494 if (vs->type != Virtual) {
495 err = "symbol after $$ must be virtual";
498 p.precedence = vs->precedence;
500 tk = token_next(state);
502 if (tk.num == TK_open) {
503 p.code = collect_code(state, tk);
504 if (p.code.txt == NULL) {
505 err = "code fragment not closed properly";
508 tk = token_next(state);
510 if (tk.num != TK_newline && tk.num != TK_eof) {
511 err = "stray tokens at end of line";
514 pp = malloc(sizeof(*pp));
516 array_add(&g->productions, &g->production_count, pp);
519 while (tk.num != TK_newline && tk.num != TK_eof)
520 tk = token_next(state);
524 With the ability to parse production and dollar-lines, we have nearly all
525 that we need to parse a grammar from a `code_node`.
527 The head of the first production will effectively be the `start` symbol of
528 the grammar. However it won't _actually_ be so. Processing the grammar is
529 greatly simplified if the real start symbol only has a single production,
530 and expects `$eof` as the final terminal. So when we find the first
531 explicit production we insert an extra production as production zero which
534 ###### Example: production 0
537 where `START` is the first non-terminal given.
539 ###### create production zero
540 struct production *p = calloc(1,sizeof(*p));
541 struct text start = {"$start",6};
542 struct text eof = {"$eof",4};
543 struct text code = {"$0 = $<1;", 9};
544 p->head = sym_find(g, start);
545 p->head->type = Nonterminal;
546 p->head->struct_name = g->current_type;
547 p->head->isref = g->type_isref;
548 if (g->current_type.txt)
550 array_add(&p->body, &p->body_size, head);
551 array_add(&p->body, &p->body_size, sym_find(g, eof));
552 p->head->first_production = g->production_count;
553 array_add(&g->productions, &g->production_count, p);
555 Now we are ready to read in the grammar.
558 static struct grammar *grammar_read(struct code_node *code)
560 struct token_config conf = {
563 .words_marks = known,
564 .known_count = sizeof(known)/sizeof(known[0]),
566 .ignored = (1 << TK_line_comment)
567 | (1 << TK_block_comment)
570 | (1 << TK_multi_string)
575 struct token_state *state = token_open(code, &conf);
577 struct symbol *head = NULL;
581 g = calloc(1, sizeof(*g));
584 for (tk = token_next(state); tk.num != TK_eof;
585 tk = token_next(state)) {
586 if (tk.num == TK_newline)
588 if (tk.num == TK_ident) {
590 head = sym_find(g, tk.txt);
591 if (head->type == Nonterminal)
592 err = "This non-terminal has already be used.";
593 else if (head->type == Virtual)
594 err = "Virtual symbol not permitted in head of production";
596 head->type = Nonterminal;
597 head->struct_name = g->current_type;
598 head->isref = g->type_isref;
599 if (g->production_count == 0) {
600 ## create production zero
602 head->first_production = g->production_count;
603 tk = token_next(state);
604 if (tk.num == TK_mark &&
605 text_is(tk.txt, "->"))
606 err = parse_production(g, head, state);
608 err = "'->' missing in production";
610 } else if (tk.num == TK_mark
611 && text_is(tk.txt, "|")) {
612 // another production for same non-term
614 err = parse_production(g, head, state);
616 err = "First production must have a head";
617 } else if (tk.num == TK_mark
618 && text_is(tk.txt, "$")) {
619 err = dollar_line(state, g, 0);
620 } else if (tk.num == TK_mark
621 && text_is(tk.txt, "$*")) {
622 err = dollar_line(state, g, 1);
624 err = "Unrecognised token at start of line.";
632 fprintf(stderr, "Error at line %d: %s\n",
639 ## Analysing the grammar
641 The central task in analysing the grammar is to determine a set of
642 states to drive the parsing process. This will require finding
643 various sets of symbols and of "items". Some of these sets will need
644 to attach information to each element in the set, so they are more
647 Each "item" may have a 'look-ahead' or `LA` set associated with
648 it. Many of these will be the same as each other. To avoid memory
649 wastage, and to simplify some comparisons of sets, these sets will be
650 stored in a list of unique sets, each assigned a number.
652 Once we have the data structures in hand to manage these sets and
653 lists, we can start setting the 'nullable' flag, build the 'FIRST'
654 sets, and then create the item sets which define the various states.
658 Though we don't only store symbols in these sets, they are the main
659 things we store, so they are called symbol sets or "symsets".
661 A symset has a size, an array of shorts, and an optional array of data
662 values, which are also shorts. If the array of data is not present,
663 we store an impossible pointer, as `NULL` is used to indicate that no
664 memory has been allocated yet;
669 unsigned short *syms, *data;
671 #define NO_DATA ((unsigned short *)1)
672 const struct symset INIT_SYMSET = { 0, NULL, NO_DATA };
673 const struct symset INIT_DATASET = { 0, NULL, NULL };
675 The arrays of shorts are allocated in blocks of 8 and are kept sorted
676 by using an insertion sort. We don't explicitly record the amount of
677 allocated space as it can be derived directly from the current `cnt` using
678 `((cnt - 1) | 7) + 1`.
681 static void symset_add(struct symset *s, unsigned short key, unsigned short val)
684 int current = ((s->cnt-1) | 7) + 1;
685 if (current == s->cnt) {
687 s->syms = realloc(s->syms, sizeof(*s->syms) * current);
688 if (s->data != NO_DATA)
689 s->data = realloc(s->data, sizeof(*s->data) * current);
692 while (i > 0 && s->syms[i-1] > key) {
693 s->syms[i] = s->syms[i-1];
694 if (s->data != NO_DATA)
695 s->data[i] = s->data[i-1];
699 if (s->data != NO_DATA)
704 Finding a symbol (or item) in a `symset` uses a simple binary search.
705 We return the index where the value was found (so data can be accessed),
706 or `-1` to indicate failure.
708 static int symset_find(struct symset *ss, unsigned short key)
715 while (lo + 1 < hi) {
716 int mid = (lo + hi) / 2;
717 if (ss->syms[mid] <= key)
722 if (ss->syms[lo] == key)
727 We will often want to form the union of two symsets. When we do, we
728 will often want to know if anything changed (as they might mean there
729 is more work to do). So `symset_union` reports whether anything was
730 added to the first set. We use a slow quadratic approach as these
731 sets don't really get very big. If profiles shows this to be a problem is
732 can be optimised later.
734 static int symset_union(struct symset *a, struct symset *b)
738 for (i = 0; i < b->cnt; i++)
739 if (symset_find(a, b->syms[i]) < 0) {
740 unsigned short data = 0;
741 if (b->data != NO_DATA)
743 symset_add(a, b->syms[i], data);
749 And of course we must be able to free a symset.
751 static void symset_free(struct symset ss)
754 if (ss.data != NO_DATA)
760 Some symsets are simply stored somewhere appropriate in the `grammar`
761 data structure, others needs a bit of indirection. This applies
762 particularly to "LA" sets. These will be paired with "items" in an
763 "itemset". As itemsets will be stored in a symset, the "LA" set needs to be
764 stored in the `data` field, so we need a mapping from a small (short)
765 number to an LA `symset`.
767 As mentioned earlier this involves creating a list of unique symsets.
769 For now, we just use a linear list sorted by insertion. A skiplist
770 would be more efficient and may be added later.
777 struct setlist *next;
780 ###### grammar fields
781 struct setlist *sets;
786 static int ss_cmp(struct symset a, struct symset b)
789 int diff = a.cnt - b.cnt;
792 for (i = 0; i < a.cnt; i++) {
793 diff = (int)a.syms[i] - (int)b.syms[i];
800 static int save_set(struct grammar *g, struct symset ss)
802 struct setlist **sl = &g->sets;
806 while (*sl && (cmp = ss_cmp((*sl)->ss, ss)) < 0)
813 s = malloc(sizeof(*s));
822 Finding a set by number is currently performed by a simple linear search.
823 If this turns out to hurt performance, we can store the sets in a dynamic
824 array like the productions.
826 static struct symset set_find(struct grammar *g, int num)
828 struct setlist *sl = g->sets;
829 while (sl && sl->num != num)
835 ### Setting `nullable`
837 We set `nullable` on the head symbol for any production for which all
838 the body symbols (if any) are nullable. As this is a recursive
839 definition, any change in the `nullable` setting means that we need to
840 re-evaluate where it needs to be set.
842 We simply loop around performing the same calculations until no more
849 static void set_nullable(struct grammar *g)
852 while (check_again) {
855 for (p = 0; p < g->production_count; p++) {
856 struct production *pr = g->productions[p];
859 if (pr->head->nullable)
861 for (s = 0; s < pr->body_size; s++)
862 if (! pr->body[s]->nullable)
864 if (s == pr->body_size) {
865 pr->head->nullable = 1;
872 ### Setting `can_eol` and `line_like`
874 In order to be able to ignore newline tokens when not relevant, but
875 still include them in the parse when needed, we will need to know
876 which states can start a "line-like" section of code. We ignore
877 newlines when there is an indent since the most recent start of a
880 To know which symbols are line-like, we first need to know which
881 symbols start with a NEWLINE token. Any symbol which is followed by a
882 NEWLINE, or anything that starts with a NEWLINE, is deemed to be a line-like symbol.
883 Certainly when trying to parse one of these we must take not of NEWLINEs.
885 Clearly the `TK_newline` token can start with a NEWLINE. Any symbol
886 which is the head of a production that contains a starts-with-NEWLINE
887 symbol preceeded only by nullable symbols is also a
888 starts-with-NEWLINE symbol. We use a new field `can_eol` to record
889 this attribute of symbols, and compute it in a repetitive manner
890 similar to `set_nullable`.
892 Once we have that, we can determine which symbols are `line_like` be
893 seeing which are followed by a `can_eol` symbol in any production.
900 static void set_can_eol(struct grammar *g)
903 g->symtab[TK_newline]->can_eol = 1;
904 while (check_again) {
907 for (p = 0; p < g->production_count; p++) {
908 struct production *pr = g->productions[p];
911 if (pr->head->can_eol)
914 for (s = 0 ; s < pr->body_size; s++) {
915 if (pr->body[s]->can_eol) {
916 pr->head->can_eol = 1;
920 if (!pr->body[s]->nullable)
927 static void set_line_like(struct grammar *g)
930 for (p = 0; p < g->production_count; p++) {
931 struct production *pr = g->productions[p];
934 for (s = 1; s < pr->body_size; s++)
935 if (pr->body[s]->can_eol)
936 pr->body[s-1]->line_like = 1;
940 ### Building the `first` sets
942 When calculating what can follow a particular non-terminal, we will need to
943 know what the "first" terminal in any subsequent non-terminal might be. So
944 we calculate the `first` set for every non-terminal and store them in an
945 array. We don't bother recording the "first" set for terminals as they are
948 As the "first" for one symbol might depend on the "first" of another,
949 we repeat the calculations until no changes happen, just like with
950 `set_nullable`. This makes use of the fact that `symset_union`
951 reports if any change happens.
953 The core of this which finds the "first" of part of a production body
954 will be reused for computing the "follow" sets, so we split it out
955 into a separate function.
957 ###### grammar fields
958 struct symset *first;
962 static int add_first(struct production *pr, int start,
963 struct symset *target, struct grammar *g,
968 for (s = start; s < pr->body_size; s++) {
969 struct symbol *bs = pr->body[s];
970 if (bs->type == Terminal) {
971 if (symset_find(target, bs->num) < 0) {
972 symset_add(target, bs->num, 0);
976 } else if (symset_union(target, &g->first[bs->num]))
982 *to_end = (s == pr->body_size);
986 static void build_first(struct grammar *g)
990 g->first = calloc(g->num_syms, sizeof(g->first[0]));
991 for (s = 0; s < g->num_syms; s++)
992 g->first[s] = INIT_SYMSET;
994 while (check_again) {
997 for (p = 0; p < g->production_count; p++) {
998 struct production *pr = g->productions[p];
999 struct symset *head = &g->first[pr->head->num];
1001 if (add_first(pr, 0, head, g, NULL))
1007 ### Building the `follow` sets.
1009 There are two different situations when we will want to generate "follow"
1010 sets. If we are doing an SLR analysis, we want to generate a single
1011 "follow" set for each non-terminal in the grammar. That is what is
1012 happening here. If we are doing an LALR or LR analysis we will want
1013 to generate a separate "LA" set for each item. We do that later
1014 in state generation.
1016 There are two parts to generating a "follow" set. Firstly we look at
1017 every place that any non-terminal appears in the body of any
1018 production, and we find the set of possible "first" symbols after
1019 there. This is done using `add_first` above and only needs to be done
1020 once as the "first" sets are now stable and will not change.
1024 for (p = 0; p < g->production_count; p++) {
1025 struct production *pr = g->productions[p];
1028 for (b = 0; b < pr->body_size - 1; b++) {
1029 struct symbol *bs = pr->body[b];
1030 if (bs->type == Terminal)
1032 add_first(pr, b+1, &g->follow[bs->num], g, NULL);
1036 The second part is to add the "follow" set of the head of a production
1037 to the "follow" sets of the final symbol in the production, and any
1038 other symbol which is followed only by `nullable` symbols. As this
1039 depends on "follow" itself we need to repeatedly perform the process
1040 until no further changes happen.
1044 for (again = 0, p = 0;
1045 p < g->production_count;
1046 p < g->production_count-1
1047 ? p++ : again ? (again = 0, p = 0)
1049 struct production *pr = g->productions[p];
1052 for (b = pr->body_size - 1; b >= 0; b--) {
1053 struct symbol *bs = pr->body[b];
1054 if (bs->type == Terminal)
1056 if (symset_union(&g->follow[bs->num],
1057 &g->follow[pr->head->num]))
1064 We now just need to create and initialise the `follow` list to get a
1067 ###### grammar fields
1068 struct symset *follow;
1071 static void build_follow(struct grammar *g)
1074 g->follow = calloc(g->num_syms, sizeof(g->follow[0]));
1075 for (s = 0; s < g->num_syms; s++)
1076 g->follow[s] = INIT_SYMSET;
1080 ### Building itemsets and states
1082 There are three different levels of detail that can be chosen for
1083 building the itemsets and states for the LR grammar. They are:
1085 1. LR(0) or SLR(1), where no look-ahead is considered.
1086 2. LALR(1) where we build look-ahead sets with each item and merge
1087 the LA sets when we find two paths to the same "kernel" set of items.
1088 3. LR(1) where different look-ahead for any item in the set means
1089 a different state must be created.
1091 ###### forward declarations
1092 enum grammar_type { LR0, LR05, SLR, LALR, LR1 };
1094 We need to be able to look through existing states to see if a newly
1095 generated state already exists. For now we use a simple sorted linked
1098 An item is a pair of numbers: the production number and the position of
1099 "DOT", which is an index into the body of the production.
1100 As the numbers are not enormous we can combine them into a single "short"
1101 and store them in a `symset` - 4 bits for "DOT" and 12 bits for the
1102 production number (so 4000 productions with maximum of 15 symbols in the
1105 Comparing the itemsets will be a little different to comparing symsets
1106 as we want to do the lookup after generating the "kernel" of an
1107 itemset, so we need to ignore the offset=zero items which are added during
1110 To facilitate this, we modify the "DOT" number so that "0" sorts to
1111 the end of the list in the symset, and then only compare items before
1115 static inline unsigned short item_num(int production, int index)
1117 return production | ((31-index) << 11);
1119 static inline int item_prod(unsigned short item)
1121 return item & 0x7ff;
1123 static inline int item_index(unsigned short item)
1125 return (31-(item >> 11)) & 0x1f;
1128 For LR(1) analysis we need to compare not just the itemset in a state
1129 but also the LA sets. As we assign each unique LA set a number, we
1130 can just compare the symset and the data values together.
1133 static int itemset_cmp(struct symset a, struct symset b,
1134 enum grammar_type type)
1140 i < a.cnt && i < b.cnt &&
1141 item_index(a.syms[i]) > 0 &&
1142 item_index(b.syms[i]) > 0;
1144 int diff = a.syms[i] - b.syms[i];
1148 diff = a.data[i] - b.data[i];
1153 if (i == a.cnt || item_index(a.syms[i]) == 0)
1157 if (i == b.cnt || item_index(b.syms[i]) == 0)
1163 if (type < LR1 || av == -1)
1166 a.data[i] - b.data[i];
1169 And now we can build the list of itemsets. The lookup routine returns
1170 both a success flag and a pointer to where in the list an insert
1171 should happen, so we don't need to search a second time.
1175 struct itemset *next;
1177 struct symset items;
1178 struct symset go_to;
1183 ###### grammar fields
1184 struct itemset *items;
1188 static int itemset_find(struct grammar *g, struct itemset ***where,
1189 struct symset kernel, enum grammar_type type)
1191 struct itemset **ip;
1193 for (ip = &g->items; *ip ; ip = & (*ip)->next) {
1194 struct itemset *i = *ip;
1196 diff = itemset_cmp(i->items, kernel, type);
1209 Adding an itemset may require merging the LA sets if LALR analysis is
1210 happening. If any new LA set adds any symbols that weren't in the old LA set, we
1211 clear the `completed` flag so that the dependants of this itemset will be
1212 recalculated and their LA sets updated.
1214 `add_itemset` must consume the symsets it is passed, either by adding
1215 them to a data structure, of freeing them.
1217 static int add_itemset(struct grammar *g, struct symset ss,
1218 enum grammar_type type)
1220 struct itemset **where, *is;
1222 int found = itemset_find(g, &where, ss, type);
1224 is = calloc(1, sizeof(*is));
1225 is->state = g->states;
1229 is->go_to = INIT_DATASET;
1238 for (i = 0; i < ss.cnt; i++) {
1239 struct symset temp = INIT_SYMSET, s;
1240 if (ss.data[i] == is->items.data[i])
1242 s = set_find(g, is->items.data[i]);
1243 symset_union(&temp, &s);
1244 s = set_find(g, ss.data[i]);
1245 if (symset_union(&temp, &s)) {
1246 is->items.data[i] = save_set(g, temp);
1257 To build all the itemsets, we first insert the initial itemset made
1258 from production zero, complete each itemset, and then generate new
1259 itemsets from old until no new ones can be made.
1261 Completing an itemset means finding all the items where "DOT" is followed by
1262 a nonterminal and adding "DOT=0" items for every production from that
1263 non-terminal - providing each item hasn't already been added.
1265 If LA sets are needed, the LA set for each new item is found using
1266 `add_first` which was developed earlier for `FIRST` and `FOLLOW`. This may
1267 be supplemented by the LA set for the item which produce the new item.
1269 We also collect a set of all symbols which follow "DOT" (in `done`) as this
1270 is used in the next stage.
1271 If any of these symbols are flagged as starting a line, then this
1272 state must be a `starts_line` state so now is a good time to record that.
1274 NOTE: precedence handling should happen here - I haven't written this yet
1277 ###### complete itemset
1278 for (i = 0; i < is->items.cnt; i++) {
1279 int p = item_prod(is->items.syms[i]);
1280 int bs = item_index(is->items.syms[i]);
1281 struct production *pr = g->productions[p];
1284 struct symset LA = INIT_SYMSET;
1285 unsigned short sn = 0;
1287 if (bs == pr->body_size)
1290 if (symset_find(&done, s->num) < 0) {
1291 symset_add(&done, s->num, 0);
1293 is->starts_line = 1;
1295 if (s->type != Nonterminal)
1301 add_first(pr, bs+1, &LA, g, &to_end);
1303 struct symset ss = set_find(g, is->items.data[i]);
1304 symset_union(&LA, &ss);
1306 sn = save_set(g, LA);
1307 LA = set_find(g, sn);
1310 /* Add productions for this symbol */
1311 for (p2 = s->first_production;
1312 p2 < g->production_count &&
1313 g->productions[p2]->head == s;
1315 int itm = item_num(p2, 0);
1316 int pos = symset_find(&is->items, itm);
1318 symset_add(&is->items, itm, sn);
1319 /* Will have re-ordered, so start
1320 * from beginning again */
1322 } else if (type >= LALR) {
1323 struct symset ss = set_find(g, is->items.data[pos]);
1324 struct symset tmp = INIT_SYMSET;
1326 symset_union(&tmp, &ss);
1327 if (symset_union(&tmp, &LA)) {
1328 is->items.data[pos] = save_set(g, tmp);
1336 For each symbol we found (and placed in `done`) we collect all the items for
1337 which this symbol is next, and create a new itemset with "DOT" advanced over
1338 the symbol. This is then added to the collection of itemsets (or merged
1339 with a pre-existing itemset).
1341 ###### derive itemsets
1342 // Now we have a completed itemset, so we need to
1343 // compute all the 'next' itemsets and create them
1344 // if they don't exist.
1345 for (i = 0; i < done.cnt; i++) {
1347 unsigned short state;
1348 struct symbol *sym = g->symtab[done.syms[i]];
1349 struct symset newitemset = INIT_SYMSET;
1351 newitemset = INIT_DATASET;
1353 for (j = 0; j < is->items.cnt; j++) {
1354 int itm = is->items.syms[j];
1355 int p = item_prod(itm);
1356 int bp = item_index(itm);
1357 struct production *pr = g->productions[p];
1358 unsigned short la = 0;
1361 if (bp == pr->body_size)
1363 if (pr->body[bp] != sym)
1366 la = is->items.data[j];
1367 pos = symset_find(&newitemset, pr->head->num);
1369 symset_add(&newitemset, item_num(p, bp+1), la);
1370 else if (type >= LALR) {
1371 // Need to merge la set.
1372 int la2 = newitemset.data[pos];
1374 struct symset ss = set_find(g, la2);
1375 struct symset LA = INIT_SYMSET;
1376 symset_union(&LA, &ss);
1377 ss = set_find(g, la);
1378 if (symset_union(&LA, &ss))
1379 newitemset.data[pos] = save_set(g, LA);
1385 state = add_itemset(g, newitemset, type);
1386 if (symset_find(&is->go_to, done.syms[i]) < 0)
1387 symset_add(&is->go_to, done.syms[i], state);
1390 All that is left is to crate the initial itemset from production zero, and
1391 with `TK_eof` as the LA set.
1394 static void build_itemsets(struct grammar *g, enum grammar_type type)
1396 struct symset first = INIT_SYMSET;
1399 unsigned short la = 0;
1401 // LA set just has eof
1402 struct symset eof = INIT_SYMSET;
1403 symset_add(&eof, TK_eof, 0);
1404 la = save_set(g, eof);
1405 first = INIT_DATASET;
1407 // production 0, offset 0 (with no data)
1408 symset_add(&first, item_num(0, 0), la);
1409 add_itemset(g, first, type);
1410 for (again = 0, is = g->items;
1412 is = is->next ?: again ? (again = 0, g->items) : NULL) {
1414 struct symset done = INIT_SYMSET;
1425 ### Completing the analysis.
1427 The exact process of analysis depends on which level was requested. For
1428 `LR0` and `LR05` we don't need first and follow sets at all. For `LALR` and
1429 `LR1` we need first, but not follow. For `SLR` we need both.
1431 We don't build the "action" tables that you might expect as the parser
1432 doesn't use them. They will be calculated to some extent if needed for
1435 Once we have built everything we allocate arrays for the two lists:
1436 symbols and itemsets. This allows more efficient access during reporting.
1437 The symbols are grouped as terminals and non-terminals and we record the
1438 changeover point in `first_nonterm`.
1440 ###### grammar fields
1441 struct symbol **symtab;
1442 struct itemset **statetab;
1445 ###### grammar_analyse
1447 static void grammar_analyse(struct grammar *g, enum grammar_type type)
1451 int snum = TK_reserved;
1452 for (s = g->syms; s; s = s->next)
1453 if (s->num < 0 && s->type == Terminal) {
1457 g->first_nonterm = snum;
1458 for (s = g->syms; s; s = s->next)
1464 g->symtab = calloc(g->num_syms, sizeof(g->symtab[0]));
1465 for (s = g->syms; s; s = s->next)
1466 g->symtab[s->num] = s;
1477 build_itemsets(g, type);
1479 g->statetab = calloc(g->states, sizeof(g->statetab[0]));
1480 for (is = g->items; is ; is = is->next)
1481 g->statetab[is->state] = is;
1484 ## Reporting on the Grammar
1486 The purpose of the report is to give the grammar developer insight into
1487 how the grammar parser will work. It is basically a structured dump of
1488 all the tables that have been generated, plus a description of any conflicts.
1490 ###### grammar_report
1491 static int grammar_report(struct grammar *g, enum grammar_type type)
1497 return report_conflicts(g, type);
1500 Firstly we have the complete list of symbols, together with the
1501 "FIRST" set if that was generated. We add a mark to each symbol to
1502 show if it can end in a newline (`>`), if it implies the start of a
1503 line (`<`), or if it is nullable (`.`).
1507 static void report_symbols(struct grammar *g)
1511 printf("SYMBOLS + FIRST:\n");
1513 printf("SYMBOLS:\n");
1515 for (n = 0; n < g->num_syms; n++) {
1516 struct symbol *s = g->symtab[n];
1520 printf(" %c%c%c%3d%c: ",
1521 s->nullable ? '.':' ',
1522 s->can_eol ? '>':' ',
1523 s->line_like ? '<':' ',
1524 s->num, symtypes[s->type]);
1527 printf(" (%d%s)", s->precedence,
1528 assoc_names[s->assoc]);
1530 if (g->first && s->type == Nonterminal) {
1533 for (j = 0; j < g->first[n].cnt; j++) {
1536 prtxt(g->symtab[g->first[n].syms[j]]->name);
1543 Then we have the follow sets if they were computed.
1545 static void report_follow(struct grammar *g)
1548 printf("FOLLOW:\n");
1549 for (n = 0; n < g->num_syms; n++)
1550 if (g->follow[n].cnt) {
1554 prtxt(g->symtab[n]->name);
1555 for (j = 0; j < g->follow[n].cnt; j++) {
1558 prtxt(g->symtab[g->follow[n].syms[j]]->name);
1564 And finally the item sets. These include the GO TO tables and, for
1565 LALR and LR1, the LA set for each item. Lots of stuff, so we break
1566 it up a bit. First the items, with production number and associativity.
1568 static void report_item(struct grammar *g, int itm)
1570 int p = item_prod(itm);
1571 int dot = item_index(itm);
1572 struct production *pr = g->productions[p];
1576 prtxt(pr->head->name);
1578 for (i = 0; i < pr->body_size; i++) {
1579 printf(" %s", (dot == i ? ". ": ""));
1580 prtxt(pr->body[i]->name);
1582 if (dot == pr->body_size)
1586 printf(" (%d%s)", pr->precedence,
1587 assoc_names[pr->assoc]);
1591 The LA sets which are (possibly) reported with each item:
1593 static void report_la(struct grammar *g, int lanum)
1595 struct symset la = set_find(g, lanum);
1599 printf(" LOOK AHEAD(%d)", lanum);
1600 for (i = 0; i < la.cnt; i++) {
1603 prtxt(g->symtab[la.syms[i]]->name);
1608 Then the go to sets:
1611 static void report_goto(struct grammar *g, struct symset gt)
1616 for (i = 0; i < gt.cnt; i++) {
1618 prtxt(g->symtab[gt.syms[i]]->name);
1619 printf(" -> %d\n", gt.data[i]);
1623 Now we can report all the item sets complete with items, LA sets, and GO TO.
1625 static void report_itemsets(struct grammar *g)
1628 printf("ITEM SETS(%d)\n", g->states);
1629 for (s = 0; s < g->states; s++) {
1631 struct itemset *is = g->statetab[s];
1632 printf(" Itemset %d:%s\n", s, is->starts_line?" (startsline)":"");
1633 for (j = 0; j < is->items.cnt; j++) {
1634 report_item(g, is->items.syms[j]);
1635 if (is->items.data != NO_DATA)
1636 report_la(g, is->items.data[j]);
1638 report_goto(g, is->go_to);
1642 ### Reporting conflicts
1644 Conflict detection varies a lot among different analysis levels. However
1645 LR0 and LR0.5 are quite similar - having no follow sets, and SLR, LALR and
1646 LR1 are also similar as they have FOLLOW or LA sets.
1650 ## conflict functions
1652 static int report_conflicts(struct grammar *g, enum grammar_type type)
1655 printf("Conflicts:\n");
1657 cnt = conflicts_lr0(g, type);
1659 cnt = conflicts_slr(g, type);
1661 printf(" - no conflicts\n");
1665 LR0 conflicts are any state which have both a reducible item and
1666 a shiftable item, or two reducible items.
1668 LR05 conflicts only occurs if two possibly reductions exist,
1669 as shifts always over-ride reductions.
1671 ###### conflict functions
1672 static int conflicts_lr0(struct grammar *g, enum grammar_type type)
1676 for (i = 0; i < g->states; i++) {
1677 struct itemset *is = g->statetab[i];
1678 int last_reduce = -1;
1679 int prev_reduce = -1;
1680 int last_shift = -1;
1684 for (j = 0; j < is->items.cnt; j++) {
1685 int itm = is->items.syms[j];
1686 int p = item_prod(itm);
1687 int bp = item_index(itm);
1688 struct production *pr = g->productions[p];
1690 if (bp == pr->body_size) {
1691 prev_reduce = last_reduce;
1695 if (pr->body[bp]->type == Terminal)
1698 if (type == LR0 && last_reduce >= 0 && last_shift >= 0) {
1699 printf(" State %d has both SHIFT and REDUCE:\n", i);
1700 report_item(g, is->items.syms[last_shift]);
1701 report_item(g, is->items.syms[last_reduce]);
1704 if (prev_reduce >= 0) {
1705 printf(" State %d has 2 (or more) reducible items\n", i);
1706 report_item(g, is->items.syms[prev_reduce]);
1707 report_item(g, is->items.syms[last_reduce]);
1714 SLR, LALR, and LR1 conflicts happen if two reducible items have over-lapping
1715 look ahead, or if a symbol in a look-ahead can be shifted. They differ only
1716 in the source of the look ahead set.
1718 We build two datasets to reflect the "action" table: one which maps
1719 terminals to items where that terminal could be shifted and another
1720 which maps terminals to items that could be reduced when the terminal
1721 is in look-ahead. We report when we get conflicts between the two.
1723 static int conflicts_slr(struct grammar *g, enum grammar_type type)
1728 for (i = 0; i < g->states; i++) {
1729 struct itemset *is = g->statetab[i];
1730 struct symset shifts = INIT_DATASET;
1731 struct symset reduce = INIT_DATASET;
1735 /* First collect the shifts */
1736 for (j = 0; j < is->items.cnt; j++) {
1737 unsigned short itm = is->items.syms[j];
1738 int p = item_prod(itm);
1739 int bp = item_index(itm);
1740 struct production *pr = g->productions[p];
1742 if (bp < pr->body_size &&
1743 pr->body[bp]->type == Terminal) {
1745 int sym = pr->body[bp]->num;
1746 if (symset_find(&shifts, sym) < 0)
1747 symset_add(&shifts, sym, itm);
1750 /* Now look for reduction and conflicts */
1751 for (j = 0; j < is->items.cnt; j++) {
1752 unsigned short itm = is->items.syms[j];
1753 int p = item_prod(itm);
1754 int bp = item_index(itm);
1755 struct production *pr = g->productions[p];
1757 if (bp < pr->body_size)
1762 la = g->follow[pr->head->num];
1764 la = set_find(g, is->items.data[j]);
1766 for (k = 0; k < la.cnt; k++) {
1767 int pos = symset_find(&shifts, la.syms[k]);
1769 printf(" State %d has SHIFT/REDUCE conflict on ", i);
1770 prtxt(g->symtab[la.syms[k]]->name);
1772 report_item(g, shifts.data[pos]);
1773 report_item(g, itm);
1776 pos = symset_find(&reduce, la.syms[k]);
1778 symset_add(&reduce, la.syms[k], itm);
1781 printf(" State %d has REDUCE/REDUCE conflict on ", i);
1782 prtxt(g->symtab[la.syms[k]]->name);
1784 report_item(g, itm);
1785 report_item(g, reduce.data[pos]);
1789 symset_free(shifts);
1790 symset_free(reduce);
1796 ## Generating the parser
1798 The exported part of the parser is the `parse_XX` function, where the name
1799 `XX` is based on the name of the parser files.
1801 This takes a `code_node`, a partially initialized `token_config`, and an
1802 optional `FILE` to send tracing to. The `token_config` gets the list of
1803 known words added and then is used with the `code_node` to initialize the
1806 `parse_XX` then calls the library function `parser_run` to actually complete
1807 the parse. This needs the `states` table and function to call the various
1808 pieces of code provided in the grammar file, so they are generated first.
1810 ###### parser_generate
1812 static void gen_parser(FILE *f, struct grammar *g, char *file, char *name)
1818 gen_reduce(f, g, file);
1821 fprintf(f, "#line 0 \"gen_parser\"\n");
1822 fprintf(f, "void *parse_%s(struct code_node *code, struct token_config *config, FILE *trace)\n",
1825 fprintf(f, "\tstruct token_state *tokens;\n");
1826 fprintf(f, "\tconfig->words_marks = known;\n");
1827 fprintf(f, "\tconfig->known_count = sizeof(known)/sizeof(known[0]);\n");
1828 fprintf(f, "\tconfig->ignored |= (1 << TK_line_comment) | (1 << TK_block_comment);\n");
1829 fprintf(f, "\ttokens = token_open(code, config);\n");
1830 fprintf(f, "\tvoid *rv = parser_run(tokens, states, do_reduce, do_free, trace, non_term, config);\n");
1831 fprintf(f, "\ttoken_close(tokens);\n");
1832 fprintf(f, "\treturn rv;\n");
1833 fprintf(f, "}\n\n");
1836 ### Known words table
1838 The known words table is simply an array of terminal symbols.
1839 The table of nonterminals used for tracing is a similar array.
1843 static void gen_known(FILE *f, struct grammar *g)
1846 fprintf(f, "#line 0 \"gen_known\"\n");
1847 fprintf(f, "static const char *known[] = {\n");
1848 for (i = TK_reserved;
1849 i < g->num_syms && g->symtab[i]->type == Terminal;
1851 fprintf(f, "\t\"%.*s\",\n", g->symtab[i]->name.len,
1852 g->symtab[i]->name.txt);
1853 fprintf(f, "};\n\n");
1856 static void gen_non_term(FILE *f, struct grammar *g)
1859 fprintf(f, "#line 0 \"gen_non_term\"\n");
1860 fprintf(f, "static const char *non_term[] = {\n");
1861 for (i = TK_reserved;
1864 if (g->symtab[i]->type == Nonterminal)
1865 fprintf(f, "\t\"%.*s\",\n", g->symtab[i]->name.len,
1866 g->symtab[i]->name.txt);
1867 fprintf(f, "};\n\n");
1870 ### States and the goto tables.
1872 For each state we record the goto table, the reducible production if
1873 there is one, or a symbol to shift for error recovery.
1874 Some of the details of the reducible production are stored in the
1875 `do_reduce` function to come later. Here we store the production number,
1876 the body size (useful for stack management) and the resulting symbol (useful
1877 for knowing how to free data later).
1879 The go to table is stored in a simple array of `sym` and corresponding
1882 ###### exported types
1890 const struct lookup * go_to;
1901 static void gen_goto(FILE *f, struct grammar *g)
1904 fprintf(f, "#line 0 \"gen_goto\"\n");
1905 for (i = 0; i < g->states; i++) {
1907 fprintf(f, "static const struct lookup goto_%d[] = {\n",
1909 struct symset gt = g->statetab[i]->go_to;
1910 for (j = 0; j < gt.cnt; j++)
1911 fprintf(f, "\t{ %d, %d },\n",
1912 gt.syms[j], gt.data[j]);
1919 static void gen_states(FILE *f, struct grammar *g)
1922 fprintf(f, "#line 0 \"gen_states\"\n");
1923 fprintf(f, "static const struct state states[] = {\n");
1924 for (i = 0; i < g->states; i++) {
1925 struct itemset *is = g->statetab[i];
1926 int j, prod = -1, prod_len;
1928 int shift_len = 0, shift_remain = 0;
1929 for (j = 0; j < is->items.cnt; j++) {
1930 int itm = is->items.syms[j];
1931 int p = item_prod(itm);
1932 int bp = item_index(itm);
1933 struct production *pr = g->productions[p];
1935 if (bp < pr->body_size) {
1936 if (shift_sym < 0 ||
1937 (shift_len == bp && shift_remain > pr->body_size - bp)) {
1938 shift_sym = pr->body[bp]->num;
1940 shift_remain = pr->body_size - bp;
1944 /* This is what we reduce */
1945 if (prod < 0 || prod_len < pr->body_size) {
1947 prod_len = pr->body_size;
1952 fprintf(f, "\t[%d] = { %d, goto_%d, %d, %d, %d, 0, %d },\n",
1953 i, is->go_to.cnt, i, prod,
1954 g->productions[prod]->body_size,
1955 g->productions[prod]->head->num,
1958 fprintf(f, "\t[%d] = { %d, goto_%d, -1, -1, -1, %d, %d },\n",
1959 i, is->go_to.cnt, i, shift_sym,
1962 fprintf(f, "};\n\n");
1965 ### The `do_reduce` function and the code
1967 When the parser engine decides to reduce a production, it calls `do_reduce`.
1968 This has two functions.
1970 Firstly, if a non-NULL `trace` file is passed, it prints out details of the
1971 production being reduced. Secondly it runs the code that was included with
1972 the production if any.
1974 This code needs to be able to store data somewhere. Rather than requiring
1975 `do_reduce` to `malloc` that "somewhere", we pass in a large buffer and have
1976 `do_reduce` return the size to be saved.
1978 In order for the code to access "global" context, we pass in the
1979 "config" pointer that was passed to parser function. If the `struct
1980 token_config` is embedded in some larger structure, the reducing code
1981 can access the larger structure using pointer manipulation.
1983 The code fragment requires translation when written out. Any `$N` needs to
1984 be converted to a reference either to that buffer (if `$0`) or to the
1985 structure returned by a previous reduction. These pointers need to be cast
1986 to the appropriate type for each access. All this is handling in
1989 `gen_code` also allows symbol references to contain a '`<`' as in '`$<2`'.
1990 This applied only to symbols with references (or pointers), not those with structures.
1991 The `<` implies that the reference it being moved out, so the object will not be
1992 automatically freed. This is equivalent to assigning `NULL` to the pointer.
1996 static void gen_code(struct production *p, FILE *f, struct grammar *g)
1999 char *used = calloc(1, p->body_size);
2002 fprintf(f, "\t\t\t");
2003 for (c = p->code.txt; c < p->code.txt + p->code.len; c++) {
2017 if (*c < '0' || *c > '9') {
2024 while (c[1] >= '0' && c[1] <= '9') {
2026 n = n * 10 + *c - '0';
2029 fprintf(f, "(*(struct %.*s*%s)ret)",
2030 p->head->struct_name.len,
2031 p->head->struct_name.txt,
2032 p->head->isref ? "*":"");
2033 else if (n > p->body_size)
2034 fprintf(f, "$%d", n);
2035 else if (p->body[n-1]->type == Terminal)
2036 fprintf(f, "(*(struct token *)body[%d])",
2038 else if (p->body[n-1]->struct_name.txt == NULL)
2039 fprintf(f, "$%d", n);
2041 fprintf(f, "(*(struct %.*s*%s)body[%d])",
2042 p->body[n-1]->struct_name.len,
2043 p->body[n-1]->struct_name.txt,
2044 p->body[n-1]->isref ? "*":"", n-1);
2049 for (i = 0; i < p->body_size; i++) {
2050 if (p->body[i]->struct_name.txt &&
2051 p->body[i]->isref &&
2053 // assume this has been copied out
2054 fprintf(f, "\t\t*(void**)body[%d] = NULL;\n", i);
2061 static void gen_reduce(FILE *f, struct grammar *g, char *file)
2064 fprintf(f, "#line 0 \"gen_reduce\"\n");
2065 fprintf(f, "static int do_reduce(int prod, void **body, struct token_config *config, void *ret)\n");
2067 fprintf(f, "\tint ret_size = 0;\n");
2069 fprintf(f, "\tswitch(prod) {\n");
2070 for (i = 0; i < g->production_count; i++) {
2071 struct production *p = g->productions[i];
2072 fprintf(f, "\tcase %d:\n", i);
2077 if (p->head->struct_name.txt)
2078 fprintf(f, "\t\tret_size = sizeof(struct %.*s%s);\n",
2079 p->head->struct_name.len,
2080 p->head->struct_name.txt,
2081 p->head->isref ? "*":"");
2083 fprintf(f, "\t\tbreak;\n");
2085 fprintf(f, "\t}\n\treturn ret_size;\n}\n\n");
2090 As each non-terminal can potentially cause a different type of data
2091 structure to be allocated and filled in, we need to be able to free it when
2094 It is particularly important to have fine control over freeing during error
2095 recovery where individual stack frames might need to be freed.
2097 For this, the grammar author is required to defined a `free_XX` function for
2098 each structure that is used by a non-terminal. `do_free` will call whichever
2099 is appropriate given a symbol number, and will call `free` (as is
2100 appropriate for tokens on any terminal symbol.
2104 static void gen_free(FILE *f, struct grammar *g)
2108 fprintf(f, "#line 0 \"gen_free\"\n");
2109 fprintf(f, "static void do_free(short sym, void *asn)\n");
2111 fprintf(f, "\tif (!asn) return;\n");
2112 fprintf(f, "\tif (sym < %d) {\n", g->first_nonterm);
2113 fprintf(f, "\t\tfree(asn);\n\t\treturn;\n\t}\n");
2114 fprintf(f, "\tswitch(sym) {\n");
2116 for (i = 0; i < g->num_syms; i++) {
2117 struct symbol *s = g->symtab[i];
2119 s->type != Nonterminal ||
2120 s->struct_name.txt == NULL)
2123 fprintf(f, "\tcase %d:\n", s->num);
2125 fprintf(f, "\t\tfree_%.*s(*(void**)asn);\n",
2127 s->struct_name.txt);
2128 fprintf(f, "\t\tfree(asn);\n");
2130 fprintf(f, "\t\tfree_%.*s(asn);\n",
2132 s->struct_name.txt);
2133 fprintf(f, "\t\tbreak;\n");
2135 fprintf(f, "\t}\n}\n\n");
2138 ## The main routine.
2140 There are three key parts to the "main" function of parsergen: processing
2141 the arguments, loading the grammar file, and dealing with the grammar.
2143 ### Argument processing.
2145 Command line options allow the selection of analysis mode, name of output
2146 file, and whether or not a report should be generated. By default we create
2147 a report only if no code output was requested.
2149 The `parse_XX` function name uses the basename of the output file which
2150 should not have a suffix (`.c`). `.c` is added to the given name for the
2151 code, and `.h` is added for the header (if header text is specifed in the
2158 static const struct option long_options[] = {
2159 { "LR0", 0, NULL, '0' },
2160 { "LR05", 0, NULL, '5' },
2161 { "SLR", 0, NULL, 'S' },
2162 { "LALR", 0, NULL, 'L' },
2163 { "LR1", 0, NULL, '1' },
2164 { "tag", 1, NULL, 't' },
2165 { "report", 0, NULL, 'R' },
2166 { "output", 1, NULL, 'o' },
2167 { NULL, 0, NULL, 0 }
2169 const char *options = "05SL1t:Ro:";
2171 ###### process arguments
2173 char *outfile = NULL;
2178 enum grammar_type type = LR05;
2179 while ((opt = getopt_long(argc, argv, options,
2180 long_options, NULL)) != -1) {
2195 outfile = optarg; break;
2197 tag = optarg; break;
2199 fprintf(stderr, "Usage: parsergen ...\n");
2204 infile = argv[optind++];
2206 fprintf(stderr, "No input file given\n");
2209 if (outfile && report == 1)
2212 if (name && strchr(name, '/'))
2213 name = strrchr(name, '/')+1;
2215 if (optind < argc) {
2216 fprintf(stderr, "Excess command line arguments\n");
2220 ### Loading the grammar file
2222 To be able to run `mdcode` and `scanner` on the grammar we need to memory
2225 One we have extracted the code (with `mdcode`) we expect to find three
2226 sections: header, code, and grammar. Anything else that is not
2227 excluded by the `--tag` option is an error.
2229 "header" and "code" are optional, though it is hard to build a working
2230 parser with neither. "grammar" must be provided.
2234 #include <sys/mman.h>
2239 static void pr_err(char *msg)
2242 fprintf(stderr, "%s\n", msg);
2246 struct section *table;
2250 fd = open(infile, O_RDONLY);
2252 fprintf(stderr, "parsergen: cannot open %s: %s\n",
2253 infile, strerror(errno));
2256 len = lseek(fd, 0, 2);
2257 file = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
2258 table = code_extract(file, file+len, pr_err);
2260 struct code_node *hdr = NULL;
2261 struct code_node *code = NULL;
2262 struct code_node *gram = NULL;
2263 for (s = table; s; s = s->next) {
2264 struct text sec = s->section;
2265 if (tag && !strip_tag(&sec, tag))
2267 if (text_is(sec, "header"))
2269 else if (text_is(sec, "code"))
2271 else if (text_is(sec, "grammar"))
2274 fprintf(stderr, "Unknown content section: %.*s\n",
2275 s->section.len, s->section.txt);
2280 ### Processing the input
2282 As we need to append an extention to a filename and then open it for
2283 writing, and we need to do this twice, it helps to have a separate function.
2287 static FILE *open_ext(char *base, char *ext)
2289 char *fn = malloc(strlen(base) + strlen(ext) + 1);
2291 strcat(strcpy(fn, base), ext);
2297 If we can read the grammar, then we analyse and optionally report on it. If
2298 the report finds conflicts we will exit with an error status.
2300 ###### process input
2301 struct grammar *g = NULL;
2303 fprintf(stderr, "No grammar section provided\n");
2306 g = grammar_read(gram);
2308 fprintf(stderr, "Failure to parse grammar\n");
2313 grammar_analyse(g, type);
2315 if (grammar_report(g, type))
2319 If a headers section is defined, we write it out and include a declaration
2320 for the `parse_XX` function so it can be used from separate code.
2322 if (rv == 0 && hdr && outfile) {
2323 FILE *f = open_ext(outfile, ".h");
2325 code_node_print(f, hdr, infile);
2326 fprintf(f, "void *parse_%s(struct code_node *code, struct token_config *config, FILE *trace);\n",
2330 fprintf(stderr, "Cannot create %s.h\n",
2336 And if all goes well and an output file was provided, we create the `.c`
2337 file with the code section (if any) and the parser tables and function.
2339 if (rv == 0 && outfile) {
2340 FILE *f = open_ext(outfile, ".c");
2343 code_node_print(f, code, infile);
2344 gen_parser(f, g, infile, name);
2347 fprintf(stderr, "Cannot create %s.c\n",
2353 And that about wraps it up. We need to set the locale so that UTF-8 is
2354 recognised properly, and link with `libicuuc` as `libmdcode` requires that.
2356 ###### File: parsergen.mk
2357 parsergen : parsergen.o libscanner.o libmdcode.o
2358 $(CC) $(CFLAGS) -o parsergen parsergen.o libscanner.o libmdcode.o -licuuc
2365 int main(int argc, char *argv[])
2370 setlocale(LC_ALL,"");
2372 ## process arguments
2379 ## The SHIFT/REDUCE parser
2381 Having analysed the grammar and generated all the tables, we only need the
2382 shift/reduce engine to bring it all together.
2384 ### Goto table lookup
2386 The parser generator has nicely provided us with goto tables sorted by
2387 symbol number. We need a binary search function to find a symbol in the
2390 ###### parser functions
2392 static int search(const struct state *l, int sym)
2395 int hi = l->go_to_cnt;
2399 while (lo + 1 < hi) {
2400 int mid = (lo + hi) / 2;
2401 if (l->go_to[mid].sym <= sym)
2406 if (l->go_to[lo].sym == sym)
2407 return l->go_to[lo].state;
2412 ### The state stack.
2414 The core data structure for the parser is the stack. This tracks all the
2415 symbols that have been recognised or partially recognised.
2417 The stack usually won't grow very large - maybe a few tens of entries. So
2418 we dynamically resize and array as required but never bother to shrink it
2421 We keep the stack as two separate allocations. One, `asn_stack` stores the
2422 "abstract syntax nodes" which are created by each reduction. When we call
2423 `do_reduce` we need to pass an array of the `asn`s of the body of the
2424 production, and by keeping a separate `asn` stack, we can just pass a
2425 pointer into this stack.
2427 The other allocation stores all other stack fields of which there are six.
2428 The `state` is the most important one and guides the parsing process. The
2429 `sym` is nearly unnecessary. However when we want to free entries from the
2430 `asn_stack`, it helps to know what type they are so we can call the right
2431 freeing function. The symbol leads us to the right free function through
2434 The `indents` count and the `starts_indented` flag track the line
2435 indents in the symbol. These are used to allow indent information to
2436 guide parsing and error recovery.
2438 `since_newline` tracks how many stack frames since the last
2439 start-of-line (whether indented or not). So if `since_newline` is
2440 zero, then this symbol is at the start of a line.
2442 `newline_permitted` keeps track of whether newlines should be ignored
2443 or not, and `starts_line` records if this state stated on a newline.
2445 The stack is most properly seen as alternating states and symbols -
2446 states, like the 'DOT' in items, are between symbols. Each frame in
2447 our stack holds a state and the symbol that was before it. The
2448 bottom of stack holds the start state, but no symbol, as nothing came
2449 before the beginning.
2451 ###### parser functions
2456 short newline_permitted;
2459 short starts_indented;
2461 short since_newline;
2470 Two operations are needed on the stack - shift (which is like push) and pop.
2472 Shift applies not only to terminals but also to non-terminals. When we
2473 reduce a production we will pop off entries corresponding to the body
2474 symbols, then push on an item for the head of the production. This last is
2475 exactly the same process as shifting in a terminal so we use the same
2476 function for both. In both cases we provide a stack frame which
2477 contains the symbol to shift and related indent information.
2479 To simplify other code we arrange for `shift` to fail if there is no `goto`
2480 state for the symbol. This is useful in basic parsing due to our design
2481 that we shift when we can, and reduce when we cannot. So the `shift`
2482 function reports if it could.
2484 `shift` is also used to push state zero onto the stack, so if the
2485 stack is empty, it always chooses zero as the next state.
2487 So `shift` finds the next state. If that succeed it extends the allocations
2488 if needed and pushes all the information onto the stacks.
2490 Newlines are permitted after a starts_line state until an internal
2491 indent. So we need to find the topmost state which `starts_line` and
2492 see if there are any indents other than immediately after it.
2496 - if state starts_line, then newlines_permitted.
2497 - if any non-initial indents, newlines not permitted
2499 ###### parser functions
2501 static int shift(struct parser *p, struct frame *next,
2503 const struct state states[])
2505 // Push an entry onto the stack
2506 int newstate = p->tos
2507 ? search(&states[p->stack[p->tos-1].state],
2512 if (p->tos >= p->stack_size) {
2513 p->stack_size += 10;
2514 p->stack = realloc(p->stack, p->stack_size
2515 * sizeof(p->stack[0]));
2516 p->asn_stack = realloc(p->asn_stack, p->stack_size
2517 * sizeof(p->asn_stack[0]));
2519 next->state = newstate;
2520 next->newline_permitted = 0;
2522 next->newline_permitted =
2523 (p->stack[p->tos-1].newline_permitted?:-1)+1;
2524 if (next->indents > next->starts_indented)
2525 next->newline_permitted = 0;
2526 if (next->indents && next->newline_permitted > 2)
2527 next->newline_permitted = 0;
2528 if (states[newstate].starts_line)
2529 next->newline_permitted = 1;
2530 if (next->since_newline) {
2532 next->since_newline = p->stack[p->tos-1].since_newline + 1;
2534 next->since_newline = 1;
2536 p->stack[p->tos] = *next;
2537 p->asn_stack[p->tos] = asn;
2542 `pop` primarily moves the top of stack (`tos`) back down the required
2543 amount and frees any `asn` entries that need to be freed. It also
2544 collects a summary of the indents in the symbols that are being
2545 removed. It is called _after_ we reduce a production, just before we
2546 `shift` the nonterminal in.
2548 `pop` is only called if there are entries to remove, so `num` is never zero.
2550 ###### parser functions
2552 static void pop(struct parser *p, int num, struct frame *next,
2553 void(*do_free)(short sym, void *asn))
2557 next->starts_indented =
2558 p->stack[p->tos].starts_indented;
2559 next->since_newline =
2560 p->stack[p->tos].since_newline;
2562 for (i = 0; i < num; i++) {
2563 next->indents += p->stack[p->tos+i].indents;
2564 do_free(p->stack[p->tos+i].sym,
2565 p->asn_stack[p->tos+i]);
2569 ### Memory allocation
2571 The `scanner` returns tokens in a local variable - we want them in allocated
2572 memory so they can live in the `asn_stack`. Similarly the `asn` produced by
2573 a reduce is in a large buffer. Both of these require some allocation and
2574 copying, hence `memdup` and `tokcopy`.
2576 ###### parser includes
2579 ###### parser functions
2581 void *memdup(void *m, int len)
2587 memcpy(ret, m, len);
2591 static struct token *tok_copy(struct token tk)
2593 struct token *new = malloc(sizeof(*new));
2598 ### The heart of the parser.
2600 Now we have the parser. If we can shift, we do, though newlines and
2601 reducing indenting may block that. If not and we can reduce we do.
2602 If the production we reduced was production zero, then we have
2603 accepted the input and can finish.
2605 We return whatever `asn` was returned by reducing production zero.
2607 If we can neither shift nor reduce we have an error to handle. We pop
2608 single entries off the stack until we can shift the `TK_error` symbol, then
2609 drop input tokens until we find one we can shift into the new error state.
2611 When we find `TK_in` and `TK_out` tokens which report indents we need
2612 to handle them directly as the grammar cannot express what we want to
2615 `TK_in` tokens are easy: we simply update the `next` stack frame to
2616 record how many indents there are and that the next token started with
2619 `TK_out` tokens must either be counted off against any pending indent,
2620 or must force reductions until there is a pending indent which isn't
2621 at the start of a production.
2623 `TK_newline` tokens are ignored precisely if there has been an indent
2624 since the last state which could have been at the start of a line.
2626 ###### parser includes
2629 void *parser_run(struct token_state *tokens,
2630 const struct state states[],
2631 int (*do_reduce)(int, void**, struct token_config*, void*),
2632 void (*do_free)(short, void*),
2633 FILE *trace, const char *non_term[],
2634 struct token_config *config)
2636 struct parser p = { 0 };
2637 struct frame next = { 0 };
2638 struct token *tk = NULL;
2642 shift(&p, &next, NULL, states);
2644 struct token *err_tk;
2645 struct frame *tos = &p.stack[p.tos-1];
2647 tk = tok_copy(token_next(tokens));
2649 parser_trace(trace, &p, &next, tk, states, non_term, config->known_count);
2651 if (next.sym == TK_in) {
2652 next.starts_indented = 1;
2654 next.since_newline = 0;
2657 parser_trace_action(trace, "Record");
2660 if (next.sym == TK_out) {
2661 if (tos->indents > tos->starts_indented ||
2662 (tos->indents == 1 &&
2663 states[tos->state].reduce_size != 1)) {
2665 if (tos->indents <= tos->starts_indented) {
2666 // no internal indent any more, reassess 'newline_permitted'
2667 if (states[tos->state].starts_line)
2668 tos->newline_permitted = 1;
2670 tos->newline_permitted = (p.stack[p.tos-2].newline_permitted ?:-1)+1;
2674 parser_trace_action(trace, "Cancel");
2677 // fall through and force a REDUCE (as 'shift'
2680 if (next.sym == TK_newline) {
2681 if (! tos->newline_permitted) {
2684 parser_trace_action(trace, "Discard");
2687 if (states[tos->state].reduce_size > 0 &&
2688 states[tos->state].reduce_size < tos->since_newline)
2691 if (shift(&p, &next, tk, states)) {
2692 next.since_newline = !(tk->num == TK_newline);
2693 next.starts_indented = 0;
2696 parser_trace_action(trace, "Shift");
2700 if (states[tos->state].reduce_prod >= 0) {
2703 const struct state *nextstate = &states[tos->state];
2704 int prod = nextstate->reduce_prod;
2705 int size = nextstate->reduce_size;
2707 static char buf[16*1024];
2709 frame.sym = nextstate->reduce_sym;
2711 body = p.asn_stack + (p.tos - size);
2713 bufsize = do_reduce(prod, body, config, buf);
2716 pop(&p, size, &frame, do_free);
2718 frame.indents = next.indents;
2719 frame.starts_indented = frame.indents;
2720 frame.since_newline = 1;
2722 next.starts_indented = 0;
2724 res = memdup(buf, bufsize);
2725 memset(buf, 0, bufsize);
2726 if (!shift(&p, &frame, res, states)) {
2727 if (prod != 0) abort();
2731 parser_trace_action(trace, "Reduce");
2734 if (tk->num == TK_out) {
2735 // Indent problem - synthesise tokens to get us
2737 struct frame frame = { 0 };
2738 fprintf(stderr, "Synthesize %d to handle indent problem\n", states[tos->state].shift_sym);
2739 frame.sym = states[tos->state].shift_sym;
2740 frame.since_newline = 1;
2741 shift(&p, &frame, tok_copy(*tk), states);
2742 // FIXME need to report this error somehow
2743 parser_trace_action(trace, "Synthesize");
2746 /* Error. We walk up the stack until we
2747 * find a state which will accept TK_error.
2748 * We then shift in TK_error and see what state
2749 * that takes us too.
2750 * Then we discard input tokens until
2751 * we find one that is acceptable.
2753 parser_trace_action(trace, "ERROR");
2755 err_tk = tok_copy(*tk);
2756 next.sym = TK_error;
2757 while (shift(&p, &next, err_tk, states) == 0
2759 // discard this state
2760 pop(&p, 1, &next, do_free);
2763 // no state accepted TK_error
2766 tos = &p.stack[p.tos-1];
2767 while (search(&states[tos->state], tk->num) < 0 &&
2768 tk->num != TK_eof) {
2770 tk = tok_copy(token_next(tokens));
2771 if (tk->num == TK_in)
2773 if (tk->num == TK_out) {
2774 if (next.indents == 0)
2779 if (p.tos == 0 && tk->num == TK_eof)
2784 pop(&p, p.tos, &next, do_free);
2790 ###### exported functions
2791 void *parser_run(struct token_state *tokens,
2792 const struct state states[],
2793 int (*do_reduce)(int, void**, struct token_config*, void*),
2794 void (*do_free)(short, void*),
2795 FILE *trace, const char *non_term[],
2796 struct token_config *config);
2800 Being able to visualize the parser in action can be invaluable when
2801 debugging the parser code, or trying to understand how the parse of a
2802 particular grammar progresses. The stack contains all the important
2803 state, so just printing out the stack every time around the parse loop
2804 can make it possible to see exactly what is happening.
2806 This doesn't explicitly show each SHIFT and REDUCE action. However they
2807 are easily deduced from the change between consecutive lines, and the
2808 details of each state can be found by cross referencing the states list
2809 in the stack with the "report" that parsergen can generate.
2811 For terminal symbols, we just dump the token. For non-terminals we
2812 print the name of the symbol. The look ahead token is reported at the
2813 end inside square brackets.
2815 ###### parser functions
2817 static char *reserved_words[] = {
2818 [TK_error] = "ERROR",
2821 [TK_newline] = "NEWLINE",
2824 static void parser_trace_state(FILE *trace, struct frame *f, const struct state states[])
2826 fprintf(trace, "(%d", f->state);
2827 if (states[f->state].starts_line)
2828 fprintf(trace, "s");
2829 if (f->newline_permitted)
2830 fprintf(trace, "n%d", f->newline_permitted);
2831 fprintf(trace, ") ");
2834 void parser_trace(FILE *trace, struct parser *p, struct frame *n,
2835 struct token *tk, const struct state states[],
2836 const char *non_term[], int knowns)
2841 for (i = 0; i < p->tos; i++) {
2842 struct frame *f = &p->stack[i];
2845 if (sym < TK_reserved &&
2846 reserved_words[sym] != NULL)
2847 fputs(reserved_words[sym], trace);
2848 else if (sym < TK_reserved + knowns) {
2849 struct token *t = p->asn_stack[i];
2850 text_dump(trace, t->txt, 20);
2852 fputs(non_term[sym - TK_reserved - knowns],
2855 fprintf(trace, "%c%d", f->starts_indented?':':'.',
2857 if (f->since_newline == 0)
2861 parser_trace_state(trace, f, states);
2863 fprintf(trace, "[");
2864 if (tk->num < TK_reserved &&
2865 reserved_words[tk->num] != NULL)
2866 fputs(reserved_words[tk->num], trace);
2868 text_dump(trace, tk->txt, 20);
2870 fprintf(trace, "%c%d", n->starts_indented?':':'.',
2872 if (n->since_newline == 0)
2877 void parser_trace_action(FILE *trace, char *action)
2880 fprintf(trace, " - %s\n", action);
2885 The obvious example for a parser is a calculator.
2887 As `scanner` provides number parsing function using `libgmp` is it not much
2888 work to perform arbitrary rational number calculations.
2890 This calculator takes one expression, or an equality test per line. The
2891 results are printed and if any equality test fails, the program exits with
2894 ###### File: parsergen.mk
2895 calc.c calc.h : parsergen parsergen.mdc
2896 ./parsergen --tag calc -o calc parsergen.mdc
2897 calc : calc.o libparser.o libscanner.o libmdcode.o libnumber.o
2898 $(CC) $(CFLAGS) -o calc calc.o libparser.o libscanner.o libmdcode.o libnumber.o -licuuc -lgmp
2903 // what do we use for a demo-grammar? A calculator of course.
2915 #include <sys/mman.h>
2920 #include "scanner.h"
2926 static void free_number(struct number *n)
2932 int main(int argc, char *argv[])
2934 int fd = open(argv[1], O_RDONLY);
2935 int len = lseek(fd, 0, 2);
2936 char *file = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
2937 struct section *s = code_extract(file, file+len, NULL);
2938 struct token_config config = {
2939 .ignored = (1 << TK_line_comment)
2940 | (1 << TK_block_comment)
2943 .number_chars = ".,_+-",
2947 parse_calc(s->code, &config, argc > 2 ? stderr : NULL);
2949 struct section *t = s->next;
2959 Session -> Session Line
2962 Line -> Expression NEWLINE ${ gmp_printf("Answer = %Qd\n", $1.val);
2963 { mpf_t fl; mpf_init2(fl, 20); mpf_set_q(fl, $1.val);
2964 gmp_printf(" or as a decimal: %Fg\n", fl);
2968 | Expression = Expression NEWLINE ${
2969 if (mpq_equal($1.val, $3.val))
2970 gmp_printf("Both equal %Qd\n", $1.val);
2972 gmp_printf("NOT EQUAL: %Qd\n != : %Qd\n",
2977 | NEWLINE ${ printf("Blank line\n"); }$
2978 | ERROR NEWLINE ${ printf("Skipped a bad line\n"); }$
2981 Expression -> Expression + Term ${ mpq_init($0.val); mpq_add($0.val, $1.val, $3.val); }$
2982 | Expression - Term ${ mpq_init($0.val); mpq_sub($0.val, $1.val, $3.val); }$
2983 | Term ${ mpq_init($0.val); mpq_set($0.val, $1.val); }$
2985 Term -> Term * Factor ${ mpq_init($0.val); mpq_mul($0.val, $1.val, $3.val); }$
2986 | Term / Factor ${ mpq_init($0.val); mpq_div($0.val, $1.val, $3.val); }$
2987 | Factor ${ mpq_init($0.val); mpq_set($0.val, $1.val); }$
2989 Factor -> NUMBER ${ if (number_parse($0.val, $0.tail, $1.txt) == 0) mpq_init($0.val); }$
2990 | ( Expression ) ${ mpq_init($0.val); mpq_set($0.val, $2.val); }$
code / ocean / blob