X-Git-Url: https://ocean-lang.org/code/?a=blobdiff_plain;f=csrc%2Fparsergen.mdc;h=02abed32520c18dcaa1d677b81529f25ec040e03;hb=025b04b80f75fd004da2b5e884b35233ede2f6f5;hp=076f3823941a20c4abb05237da892bc726d70266;hpb=212f45a62c9e8a05a5df6b9e933619a86a9bd05b;p=ocean diff --git a/csrc/parsergen.mdc b/csrc/parsergen.mdc index 076f382..02abed3 100644 --- a/csrc/parsergen.mdc +++ b/csrc/parsergen.mdc @@ -1191,10 +1191,27 @@ And now we can build the list of itemsets. The lookup routine returns both a success flag and a pointer to where in the list an insert should happen, so we don't need to search a second time. +Each state will often have at most one reducible production, but +occasionally will have more. If there are more we will need a full +action table (merged in the go to table). If there is one, we record it +in the state. If none, we record that too. These special values will +be needed both in the generator and in the parser, so they need to be +declared twice. + +###### exported types + enum { + NONE_REDUCIBLE = -1, + MANY_REDUCIBLE = -2, + }; ###### declarations + enum { + NONE_REDUCIBLE = -1, + MANY_REDUCIBLE = -2, + }; struct itemset { struct itemset *next; short state; + short reducible_prod; /* or NONE_REDUCIBLE or MANY_REDUCIBLE */ struct symset items; struct symset go_to; enum assoc assoc; @@ -1318,8 +1335,15 @@ so the item is ineffective. struct symset LA = INIT_SYMSET; unsigned short sn = 0; - if (bs == pr->body_size) + if (i == 0) + is->reducible_prod = NONE_REDUCIBLE; + if (bs == pr->body_size) { + if (is->reducible_prod == NONE_REDUCIBLE) + is->reducible_prod = p; + else + is->reducible_prod = MANY_REDUCIBLE; continue; + } s = pr->body[bs]; if (s->precedence && is->precedence && is->precedence > s->precedence) @@ -1888,6 +1912,7 @@ grammar file, so they are generated first. { gen_known(f, g); gen_non_term(f, g); + gen_action(f, g); gen_goto(f, g); gen_states(f, g); gen_reductions(f, g); @@ -1943,6 +1968,53 @@ The table of nonterminals used for tracing is a similar array. fprintf(f, "};\n\n"); } +### The Action table + +For this parser we do not have a separate action table. The action +table normally maps terminals to one of the actions SHIFT, REDUCE(p), or +ACCEPT. We can find which terminals to SHIFT via a lookup in the go to +table, and most states have at most one reducible production and in that +case to effect that reduction for any non-shiftable terminal in the +look-ahead. + +However, with SLR, LALR, and canonical-LR grammars, there may +occasionally be multiple possible reductions which we choose between +based on the look-ahead. To handle this possibility we allow reductions +to be stored in the go to table. An extra flag indicates if an entry is +a state to go to, or a production to reduce. We add the entries with +that flag here, if necessary. + +###### functions + #define IS_REDUCTION (0x8000) + + static void gen_action(FILE *f, struct grammar *g) + { + int i, j, k; + for (i = 0; i < g->states; i++) { + struct itemset *is = g->statetab[i]; + struct symset *gt = &is->go_to; + + if (is->reducible_prod != MANY_REDUCIBLE) + continue; + for (j = 0; j < is->items.cnt; j++) { + int itm = is->items.syms[j]; + int p = item_prod(itm); + int bp = item_dot(itm); + struct production *pr = g->productions[p]; + struct symset la; + if (bp != pr->body_size) + continue; + /* This is a reducible item */ + if (g->follow) + la = g->follow[pr->head->num]; + else + la = set_find(g, is->items.data[j]); + for (k = 0 ; k < la.cnt; k++) + symset_add(gt, la.syms[k], p | IS_REDUCTION); + } + } + } + ### States, reductions, and the go to tables. For each state we record the go to table and the reducible production if @@ -1961,7 +2033,8 @@ The go to table is stored in a simple array of `sym` and corresponding struct lookup { short sym; - short state; + short state_or_reduction:15; + unsigned short is_reduction:1; }; struct reduction { short size; @@ -1969,9 +2042,9 @@ The go to table is stored in a simple array of `sym` and corresponding short result_size; }; struct state { + short reduce_prod; // or NONE_REDUCIBLE or MANY_REDUCIBLE short go_to_cnt; - const struct lookup * go_to; - short reduce_prod; + const struct lookup * go_to; // includes reductions }; ###### functions @@ -1988,9 +2061,14 @@ The go to table is stored in a simple array of `sym` and corresponding continue; fprintf(f, "static const struct lookup goto_%d[] = {\n", i); - for (j = 0; j < gt.cnt; j++) - fprintf(f, "\t{ %d, %d },\n", - gt.syms[j], gt.data[j]); + for (j = 0; j < gt.cnt; j++) { + if (gt.data[j] & IS_REDUCTION) + fprintf(f, "\t{ %d, %d, 1 },\n", + gt.syms[j], gt.data[j]&~IS_REDUCTION); + else + fprintf(f, "\t{ %d, %d, 0 },\n", + gt.syms[j], gt.data[j]); + } fprintf(f, "};\n"); } } @@ -2022,27 +2100,13 @@ The go to table is stored in a simple array of `sym` and corresponding fprintf(f, "static const struct state states[] = {\n"); for (i = 0; i < g->states; i++) { struct itemset *is = g->statetab[i]; - int j, prod = -1, prod_len; - - for (j = 0; j < is->items.cnt; j++) { - int itm = is->items.syms[j]; - int p = item_prod(itm); - int bp = item_dot(itm); - struct production *pr = g->productions[p]; + int prod = is->reducible_prod; - if (bp < pr->body_size) - continue; - /* This is what we reduce - choose longest */ - if (prod < 0 || prod_len < pr->body_size) { - prod = p; - prod_len = pr->body_size; - } - } if (is->go_to.cnt) - fprintf(f, "\t[%d] = { %d, goto_%d, %d },\n", - i, is->go_to.cnt, i, prod); + fprintf(f, "\t[%d] = { %d, %d, goto_%d },\n", + i, prod, is->go_to.cnt, i); else - fprintf(f, "\t[%d] = { 0, NULL, %d },\n", i, prod); + fprintf(f, "\t[%d] = { %d, 0, NULL },\n", i, prod); } fprintf(f, "};\n\n"); } @@ -2220,17 +2284,17 @@ transformed, and will cause an error when the code is compiled. } c -= 1; } - fputs("\n", f); for (i = 0; i < p->body_size; i++) { if (p->body[i]->struct_name.txt && used[i]) { // assume this has been copied out if (p->body[i]->isref) - fprintf(f, "\t\t*(void**)body[%d] = NULL;\n", i); + fprintf(f, "\t\t*(void**)body[%d] = NULL;", i); else - fprintf(f, "\t\tmemset(body[%d], 0, sizeof(struct %.*s));\n", i, p->body[i]->struct_name.len, p->body[i]->struct_name.txt); + fprintf(f, "\t\tmemset(body[%d], 0, sizeof(struct %.*s));", i, p->body[i]->struct_name.len, p->body[i]->struct_name.txt); } } + fputs("\n", f); free(used); } @@ -2256,6 +2320,7 @@ transformed, and will cause an error when the code is compiled. if (p->code.txt) { fprintf(f, "#line %d \"%s\"\n", p->code_line, file); gen_code(p, f, g); + fprintf(f, "#line 7 \"gen_reduce\"\n"); } if (p->head->struct_name.txt) @@ -2584,7 +2649,7 @@ table. ###### parser functions - static int search(const struct state *l, int sym) + static int search(const struct state *l, int sym, int reduction) { int lo = 0; int hi = l->go_to_cnt; @@ -2598,10 +2663,11 @@ table. else hi = mid; } - if (l->go_to[lo].sym == sym) - return l->go_to[lo].state; - else + if (l->go_to[lo].sym != sym) return -1; + if (!reduction == !l->go_to[lo].is_reduction) + return l->go_to[lo].state_or_reduction; + return -1; } ### Memory allocation @@ -2688,25 +2754,6 @@ stack is empty, it always chooses zero as the next state. So `shift` finds the next state. If that succeeds it extends the allocations if needed and pushes all the information onto the stacks. -An extra complication is added to `shift` by the `EOL` token. This -token must be generated when a `NEWLINE` is seen, but an `EOL` is -expected. When this happens, the `NEWLINE` is NOT consumed, so multiple -EOL can appear before a NEWLINE. To indicate that the token was shifted -by not consumed, `shift` can return the special value `2`. The token -number for `EOL` cannot be statically declared, so when the parser -starts we need to look through the array of non-terminals to find the -EOL. - -###### parser state - int tk_eol; - -###### find eol - p.tk_eol = 0; - while (strcmp(non_term[p.tk_eol], "EOL") != 0) - p.tk_eol += 1; - p.tk_eol += TK_reserved + config->known_count; - - ###### parser functions static int shift(struct parser *p, @@ -2714,27 +2761,12 @@ EOL. const struct state states[]) { struct frame next = {0}; - int ret; int newstate = p->tos ? search(&states[p->stack[p->tos-1].state], - sym) + sym, 0) : 0; - if (newstate >= 0) - ret = 1; - else if (sym != TK_newline) + if (newstate < 0) return 0; - else { - // have a NEWLINE, might need an EOL - sym = p->tk_eol; - newstate = p->tos - ? search(&states[p->stack[p->tos-1].state], - sym) - : 0; - if (newstate < 0) - return 0; - ret = 2; - asn = tok_copy(*(struct token*)asn); - } if (p->tos >= p->stack_size) { p->stack_size += 10; @@ -2749,7 +2781,7 @@ EOL. p->stack[p->tos] = next; p->asn_stack[p->tos] = asn; p->tos++; - return ret; + return 1; } `pop` primarily moves the top of stack (`tos`) back down the required @@ -2807,9 +2839,27 @@ of indentation. ###### parser state unsigned long ignored_indents; -NEWLINE/EOL is ignored when in an indented section of text which was not +NEWLINE is ignored when in an indented section of text which was not explicitly expected by the grammar. So if the most recent indent is -ignored, so is any EOL token. +ignored, so is any NEWLINE token. + +If a NEWLINE is seen but it cannot be shifted, we try to shift an EOL +token instead. If that succeeds, we make a new copy of the NEWLINE +token and continue. This allows a NEWLINE to appear to be preceded by +an indefinite number of EOL tokens. + +The token number for `EOL` cannot be statically declared, so when the +parser starts we need to look through the array of non-terminals to find +the EOL. + +###### parser state + int tk_eol; + +###### find eol + p.tk_eol = 0; + while (strcmp(non_term[p.tk_eol], "EOL") != 0) + p.tk_eol += 1; + p.tk_eol += TK_reserved + config->known_count; For other tokens, we shift the next token if that is possible, otherwise we try to reduce a production. @@ -2827,29 +2877,42 @@ we try to reduce a production. continue; } - switch (shift(&p, tk->num, tk, states)) { - case 1: + if (shift(&p, tk->num, tk, states)) { if (tk->num == TK_out) p.ignored_indents >>= 1; if (tk->num == TK_in) p.ignored_indents <<= 1; + parser_trace_action(trace, "Shift"); tk = NULL; - /* fallthrough */ - case 2: - parser_trace_action(trace, tk ? "ShiftEOL" : "Shift"); ## did shift continue; + } else if (tk->num == TK_newline && + shift(&p, p.tk_eol, tk, states)) { + tk = tok_copy(*tk); + parser_trace_action(trace, "ShiftEOL"); + continue; } - if (tk->num == TK_in && states[p.stack[p.tos-1].state].go_to_cnt > 0) { - /* No indent expected here and reduce is not mandatory, so ignore IN */ - free(tk); - tk = NULL; - p.ignored_indents <<= 1; - p.ignored_indents |= 1; - parser_trace_action(trace, "Ignore"); - continue; + if (tk->num == TK_in) { + int should_reduce; + if (states[tos->state].reduce_prod == MANY_REDUCIBLE) + /* Only reduce if TK_in in lookahead */ + should_reduce = (search(&states[tos->state], TK_in, 1) >= 0); + else + /* Only reduce if we cannot shift anything */ + should_reduce = (states[tos->state].go_to_cnt == 0); + if (!should_reduce) { + /* No indent expected here and reduce is not indicated, + * so ignore IN + */ + free(tk); + tk = NULL; + p.ignored_indents <<= 1; + p.ignored_indents |= 1; + parser_trace_action(trace, "Ignore"); + continue; + } } We have already discussed the bulk of the handling of a "reduce" action, @@ -2865,24 +2928,26 @@ report that that input has been accepted. ###### parser vars void *ret = NULL; + int reduction; ###### try reduce - if (states[tos->state].reduce_prod >= 0) { + reduction = states[tos->state].reduce_prod; + if (reduction == MANY_REDUCIBLE) + reduction = search(&states[tos->state], tk->num, 1); + if (reduction >= 0) { void **body; void *res; - const struct state *nextstate = &states[tos->state]; - int prod = nextstate->reduce_prod; - int size = reductions[prod].size; - int res_size = reductions[prod].result_size; + int size = reductions[reduction].size; + int res_size = reductions[reduction].result_size; body = p.asn_stack + (p.tos - size); res = res_size ? calloc(1, res_size) : NULL; - res_size = do_reduce(prod, body, config, res); - if (res_size != reductions[prod].result_size) + res_size = do_reduce(reduction, body, config, res); + if (res_size != reductions[reduction].result_size) abort(); pop(&p, size, do_free); - if (!shift(&p, reductions[prod].sym, res, states)) { + if (!shift(&p, reductions[reduction].sym, res, states)) { accepted = 1; ret = res; parser_trace_action(trace, "Accept"); @@ -3176,3 +3241,73 @@ exits with an error. 355//113 error + +## A second example + +I had originally thought that the LR05 style grammar would suit me there +should never be a sequence of token that means either of two different +things depending on what comes follows it. Without that ambiguity, the +extra strength of LALR, or even SLR, would not be needed. However I +discovered this was too simplistic. There are times when it is quite +reasonable for the empty string, or maybe a NEWLINE, to have different +meanings depending on the next token. For this, LR05 is not sufficient, +so I added full action-table support. + +This example tests the selection of REDUCE actions based on the +look-ahead symbol, using a trivial grammar where the empty string can +reasonably mean different things depending on what it precedes. + + +####### File: parsergen.mk + demos :: do_lalr_demo + lalr_demo.c lalr_demo.h : parsergen parsergen.mdc + ./parsergen --LALR --tag demo -o lalr_demo parsergen.mdc + lalr_demo: lalr_demo.o libparser.o libscanner.o libmdcode.o + $(CC) -o lalr_demo lalr_demo.c libparser.o libscanner.o libmdcode.o -licuuc + do_lalr_demo: lalr_demo + NOTRACE=1 ./lalr_demo + @echo 'Should produce "start of line, empty sign, empty sigl"' + +####### demo: grammar + + $TERM $ @ + - + line -> ${ printf("start of line"); }$ + | line term + term -> sigl IDENTIFIER + | sign NUMBER + sigl -> $ + | @ + | ${ printf(", empty sigl"); }$ + sign -> + + | - + | ${ printf(", empty sign"); }$ + +####### demo: header + + // + +####### demo: code + + #include + #include + #include "mdcode.h" + #include "scanner.h" + #include "parser.h" + #include "lalr_demo.h" + int main(int argc, char *argv[]) + { + char test[] = "````\n$a -1 5 b\n"; + struct section *table = code_extract(test, test+sizeof(test)-1, NULL); + struct token_config config = { + .ignored = (1 << TK_line_comment) + | (1 << TK_newline) + | (1 << TK_in) + | (1 << TK_out), + .number_chars = "", + .word_start = "", + .word_cont = "", + }; + parse_lalr_demo(table->code, &config, getenv("NOTRACE") ? NULL : stderr); + printf("\n"); + exit(0); + }