add LALR conflict resolution (untested)
This commit is contained in:
Sven M. Hallberg
parent
ddfd3796a7
commit
fd297b636c
3 changed files with 138 additions and 38 deletions
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@ -52,6 +52,13 @@ typedef struct HLRTable_ {
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HAllocator *mm__;
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} HLRTable;
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typedef struct HLREnhGrammar_ {
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HCFGrammar *grammar; // enhanced grammar
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HHashTable *tmap; // maps transitions to enhanced-grammar symbols
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HHashTable *smap; // maps enhanced-grammar symbols to transitions
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HArena *arena;
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} HLREnhGrammar;
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// compare symbols - terminals by value, others by pointer
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static bool eq_symbol(const void *p, const void *q)
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@ -410,14 +417,10 @@ static HLRAction *reduce_action(HArena *arena, const HLRItem *item)
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return action;
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}
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HLRTable *h_lr0_table(HCFGrammar *g)
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HLRTable *h_lr0_table(HCFGrammar *g, const HLRDFA *dfa)
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{
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HAllocator *mm__ = g->mm__;
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// construct LR(0) DFA
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HLRDFA *dfa = h_lr0_dfa(g);
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if(!dfa) return NULL;
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HLRTable *table = h_lrtable_new(mm__, dfa->nstates);
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HArena *arena = table->arena;
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@ -475,13 +478,13 @@ static size_t follow_transition(const HLRTable *table, size_t x, HCFChoice *A)
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return action->nextstate;
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}
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static HCFChoice *transform_symbol(const HLRTable *table, HHashTable *map,
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static HCFChoice *transform_symbol(const HLRTable *table, HLREnhGrammar *eg,
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size_t x, HCFChoice *B, size_t z);
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static HCFChoice *transform_productions(const HLRTable *table, HHashTable *map,
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static HCFChoice *transform_productions(const HLRTable *table, HLREnhGrammar *eg,
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size_t x, HCFChoice *xAy)
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{
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HArena *arena = map->arena;
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HArena *arena = eg->arena;
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HCFSequence **seq = h_arena_malloc(arena, seqsize(xAy->seq)
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* sizeof(HCFSequence *));
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@ -494,7 +497,7 @@ static HCFChoice *transform_productions(const HLRTable *table, HHashTable *map,
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HCFChoice **xBz = h_arena_malloc(arena, seqsize(B) * sizeof(HCFChoice *));
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for(; *B; B++, xBz++) {
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size_t z = follow_transition(table, x, *B);
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*xBz = transform_symbol(table, map, x, *B, z);
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*xBz = transform_symbol(table, eg, x, *B, z);
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x=z;
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}
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*xBz = NULL;
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@ -518,21 +521,22 @@ static inline HLRTransition *transition(HArena *arena,
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return t;
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}
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static HCFChoice *transform_symbol(const HLRTable *table, HHashTable *map,
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static HCFChoice *transform_symbol(const HLRTable *table, HLREnhGrammar *eg,
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size_t x, HCFChoice *B, size_t z)
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{
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HArena *arena = map->arena;
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HArena *arena = eg->arena;
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// look up the transition in map, create symbol if not found
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HLRTransition *x_B_z = transition(arena, x, B, z);
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HCFChoice *xBz = h_hashtable_get(map, x_B_z);
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HCFChoice *xBz = h_hashtable_get(eg->tmap, x_B_z);
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if(!xBz) {
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HCFChoice *xBz = h_arena_malloc(arena, sizeof(HCFChoice));
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*xBz = *B;
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h_hashtable_put(map, x_B_z, xBz);
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h_hashtable_put(eg->tmap, x_B_z, xBz);
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h_hashtable_put(eg->smap, xBz, x_B_z);
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}
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return transform_productions(table, map, x, xBz);
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return transform_productions(table, eg, x, xBz);
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}
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static bool eq_transition(const void *p, const void *q)
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@ -547,39 +551,71 @@ static HHashValue hash_transition(const void *p)
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return (h_hash_ptr(t->symbol) + t->from + t->to); // XXX ?
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}
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static HHashTable *enhance_grammar(const HCFGrammar *g, const HLRTable *tbl)
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static HLREnhGrammar *enhance_grammar(const HCFGrammar *g, const HLRTable *tbl)
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{
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HAllocator *mm__ = g->mm__;
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HArena *arena = g->arena; // XXX ?
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HHashTable *map = h_hashtable_new(arena, eq_transition, hash_transition);
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HLREnhGrammar *eg = h_arena_malloc(arena, sizeof(HLREnhGrammar));
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eg->tmap = h_hashtable_new(arena, eq_transition, hash_transition);
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eg->smap = h_hashtable_new(arena, eq_transition, hash_transition);
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eg->arena = arena;
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// copy the start symbol over
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HCFChoice *start = h_arena_malloc(arena, sizeof(HCFChoice));
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*start = *(g->start);
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h_hashtable_put(map, g->start, start);
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transform_productions(tbl, map, 0, start);
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transform_productions(tbl, eg, 0, start);
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return map;
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eg->grammar = h_cfgrammar_(mm__, start);
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return eg;
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}
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/* LALR table generation */
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bool is_inadequate(HLRTable *table, size_t state)
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{
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// XXX
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return false;
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}
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bool has_conflicts(HLRTable *table)
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static inline bool has_conflicts(HLRTable *table)
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{
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return !h_slist_empty(table->inadeq);
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}
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// place a new entry in tbl; records conflicts in tbl->inadeq
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// returns 0 on success, -1 on conflict
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// ignores forall entries
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int h_lrtable_put(HLRTable *tbl, size_t state, HCFChoice *x, HLRAction *action)
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{
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HLRAction *prev = h_hashtable_get(tbl->rows[state], x);
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if(prev && prev != action) {
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// conflict
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h_slist_push(tbl->inadeq, (void *)(uintptr_t)state);
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return -1;
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} else {
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h_hashtable_put(tbl->rows[state], x, action);
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return 0;
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}
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}
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// check whether a sequence of enhanced-grammar symbols (p) matches the given
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// (original-grammar) production rhs and terminates in the given end state.
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bool match_production(HLREnhGrammar *eg, HCFChoice **p,
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HCFChoice **rhs, size_t endstate)
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{
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HLRTransition *t;
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for(; *p && *rhs; p++, rhs++) {
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t = h_hashtable_get(eg->smap, *p);
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assert(t != NULL);
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if(!eq_symbol(t->symbol, *rhs))
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return false;
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}
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return (*p == *rhs // both NULL
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&& t->to == endstate);
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}
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int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params)
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{
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// generate CFG from parser
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// construct LR(0) DFA
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// build LR(0) table
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// if necessary, resolve conflicts "by conversion to SLR"
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@ -587,21 +623,79 @@ int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params)
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if(g == NULL) // backend not suitable (language not context-free)
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return -1;
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HLRTable *table = h_lr0_table(g);
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if(table == NULL) // this should normally not happen
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HLRDFA *dfa = h_lr0_dfa(g);
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if(dfa == NULL) { // this should normally not happen
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h_cfgrammar_free(g);
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return -1;
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}
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HLRTable *table = h_lr0_table(g, dfa);
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if(table == NULL) { // this should normally not happen
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h_cfgrammar_free(g);
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return -1;
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}
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if(has_conflicts(table)) {
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HHashTable *map = enhance_grammar(g, table);
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if(map == NULL) // this should normally not happen
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return -1;
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HArena *arena = table->arena;
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// XXX resolve conflicts
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// iterate over dfa's transitions where 'from' state is inadequate
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// look up enhanced symbol corr. to the transition
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// for each terminal in follow set of enh. symbol:
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// put reduce action into table cell (state, terminal)
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// conflict if already occupied
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HLREnhGrammar *eg = enhance_grammar(g, table);
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if(eg == NULL) { // this should normally not happen
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h_cfgrammar_free(g);
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h_lrtable_free(table);
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return -1;
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}
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// go through the inadequate states; replace inadeq with a new list
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HSlist *inadeq = table->inadeq;
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table->inadeq = h_slist_new(arena);
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for(HSlistNode *x=inadeq->head; x; x=x->next) {
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size_t state = (uintptr_t)x->elem;
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// clear old forall entry, it's being replaced by more fine-grained ones
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table->forall[state] = NULL;
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// go through each reducible item of state
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H_FOREACH_KEY(dfa->states[state], HLRItem *item)
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if(item->mark < item->len)
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continue;
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// action to place in the table cells indicated by lookahead
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HLRAction *action = reduce_action(arena, item);
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// find all LR(0)-enhanced productions matching item
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H_FOREACH(eg->smap, HCFChoice *lhs, HLRTransition *t)
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if(t->symbol != item->lhs)
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continue;
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for(HCFSequence **p=lhs->seq; *p; p++) {
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HCFChoice **rhs = (*p)->items;
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if(!match_production(eg, rhs, item->rhs, state))
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continue;
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// the left-hand symbol's follow set is this production's
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// contribution to the lookahead
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const HStringMap *fs = h_follow(1, eg->grammar, lhs);
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assert(fs != NULL);
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// for each lookahead symbol, put action into table cell
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if(fs->end_branch) {
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HCFChoice *terminal = h_arena_malloc(arena, sizeof(HCFChoice));
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terminal->type = HCF_END;
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h_lrtable_put(table, state, terminal, action);
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}
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H_FOREACH(fs->char_branches, void *key, HStringMap *m)
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if(!m->epsilon_branch)
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continue;
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HCFChoice *terminal = h_arena_malloc(arena, sizeof(HCFChoice));
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terminal->type = HCF_CHAR;
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terminal->chr = key_char((HCharKey)key);
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h_lrtable_put(table, state, terminal, action);
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H_END_FOREACH // lookahead character
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} H_END_FOREACH // enhanced production
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H_END_FOREACH // reducible item
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}
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}
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h_cfgrammar_free(g);
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@ -924,7 +1018,7 @@ int test_lalr(void)
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fprintf(stderr, "h_lalr_dfa failed\n");
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printf("\n==== L R ( 0 ) T A B L E ====\n");
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HLRTable *table0 = h_lr0_table(g);
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HLRTable *table0 = h_lr0_table(g, dfa);
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if(table0)
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h_pprint_lrtable(stdout, g, table0, 0);
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else
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