From dabe4b07a94835041aee26f98b5c7e594767f1a2 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Mon, 10 Jun 2013 00:46:03 +0200
Subject: [PATCH] wip end-of-day commit - almost there (untested)
---
src/backends/lalr.c | 320 +++++++++++++++++++++++++++++++++-----------
1 file changed, 242 insertions(+), 78 deletions(-)
diff --git a/src/backends/lalr.c b/src/backends/lalr.c
index b3d9b5bb..541a69af 100644
--- a/src/backends/lalr.c
+++ b/src/backends/lalr.c
@@ -4,7 +4,8 @@
#include "../parsers/parser_internal.h"
-/* Constructing the characteristic automaton (handle recognizer) */
+
+/* Data structures */
// - states are hashsets containing LRItems
// - LRItems contain an optional lookahead set (HStringMap)
@@ -19,8 +20,9 @@ typedef struct HLRDFA_ {
} HLRDFA;
typedef struct HLRTransition_ {
- size_t from, to; // indices into 'states' array
+ size_t from; // index into 'states' array
const HCFChoice *symbol;
+ size_t to; // index into 'states' array
} HLRTransition;
typedef struct HLRItem_ {
@@ -31,6 +33,32 @@ typedef struct HLRItem_ {
HStringMap *lookahead; // optional
} HLRItem;
+typedef struct HLRAction_ {
+ enum {HLR_SHIFT, HLR_REDUCE} type;
+ union {
+ size_t nextstate; // used with SHIFT
+ struct {
+ HCFChoice *lhs; // symbol carrying semantic actions etc.
+ size_t length; // # of symbols in rhs
+ // NB: the rhs symbols are not needed for the parse
+ } production; // used with REDUCE
+ };
+} HLRAction;
+
+typedef struct HLRTable_ {
+ size_t nrows;
+ HHashTable **rows; // map symbols to HLRActions
+ HLRAction **forall; // shortcut to set an action for an entire row
+ HCFChoice *start; // start symbol
+ HSlist *inadeq; // indices of any inadequate states
+ HArena *arena;
+ HAllocator *mm__;
+} HLRTable;
+
+
+
+/* Constructing the characteristic automaton (handle recognizer) */
+
HLRItem *h_lritem_new(HArena *a, HCFChoice *lhs, HCFChoice **rhs, size_t mark)
{
HLRItem *ret = h_arena_malloc(a, sizeof(HLRItem));
@@ -157,7 +185,7 @@ static HHashSet *closure(HCFGrammar *g, const HHashSet *items)
return ret;
}
-HLRDFA *h_lalr_dfa(HCFGrammar *g)
+HLRDFA *h_lr0_dfa(HCFGrammar *g)
{
HArena *arena = g->arena;
@@ -275,26 +303,24 @@ HLRDFA *h_lalr_dfa(HCFGrammar *g)
-/* LALR table generation */
+/* LR(0) table generation */
-typedef struct HLRAction_ {
- enum {HLR_SHIFT, HLR_REDUCE} type;
- union {
- size_t nextstate; // used with shift
- struct {
- HCFChoice *lhs;
- HCFChoice **rhs;
- } production; // used with reduce
- };
-} HLRAction;
+// XXX replace other hashtable iterations with this
+// XXX move to internal.h or something
+#define H_FOREACH_(HT) do { \
+ const HHashTable *ht = HT; \
+ for(size_t i=0; i < ht->capacity; i++) { \
+ for(HHashTableEntry *hte = &ht->contents[i]; hte; hte = hte->next) { \
+ if(hte->key == NULL) continue;
-typedef struct HLRTable_ {
- size_t nrows;
- HHashTable **rows; // map symbols to HLRActions
- HCFChoice *start; // start symbol
- HArena *arena;
- HAllocator *mm__;
-} HLRTable;
+#define H_FOREACH(HT, KEYVAR, VALVAR) H_FOREACH_(HT) \
+ const KEYVAR = hte->key; \
+ VALVAR = hte->value;
+
+#define H_END_FOREACH \
+ } \
+ } \
+ } while(0);
HLRTable *h_lrtable_new(HAllocator *mm__, size_t nrows)
{
@@ -313,91 +339,229 @@ HLRTable *h_lrtable_new(HAllocator *mm__, size_t nrows)
return ret;
}
-static HCFGrammar *transform_grammar(const HCFGrammar *g, const HLRTable *table,
- const HLRDFA *dfa, HHashTable **syms)
+void h_lrtable_free(HLRTable *table)
{
- HCFGrammar *gt = h_cfgrammar_new(g->mm__);
- HArena *arena = gt->arena;
+ HAllocator *mm__ = table->mm__;
+ h_delete_arena(table->arena);
+ h_free(table);
+}
- // old grammar symbol ->
- //HHashTable *map = h_hashtable_new(
+static HLRAction *shift_action(HArena *arena, size_t nextstate)
+{
+ HLRAction *action = h_arena_malloc(arena, sizeof(HLRAction));
+ action->type = HLR_SHIFT;
+ action->nextstate = nextstate;
+ return action;
+}
- for(size_t i=0; i<dfa->nstates; i++) {
- const HLRState *state = dfa->states[i];
+static HLRAction *reduce_action(HArena *arena, HCFChoice *lhs, size_t rhslen)
+{
+ HLRAction *action = h_arena_malloc(arena, sizeof(HLRAction));
+ action->type = HLR_REDUCE;
+ action->production.lhs = lhs;
+ action->production.length = rhslen;
+ return action;
+}
- syms[i] = h_hashtable_new(arena, h_eq_ptr, h_hash_ptr);
-
-
- }
+HLRTable *h_lr0_table(HCFGrammar *g)
+{
+ HAllocator *mm__ = g->mm__;
- // iterate over g->nts
- const HHashTable *ht = g->nts;
- for(size_t i=0; i < ht->capacity; i++) {
- for(HHashTableEntry *hte = &ht->contents[i]; hte; hte = hte->next) {
- if(hte->key == NULL)
- continue;
+ // construct LR(0) DFA
+ HLRDFA *dfa = h_lr0_dfa(g);
+ if(!dfa) return NULL;
+
+ HLRTable *table = h_lrtable_new(mm__, dfa->nstates);
+ HArena *arena = table->arena;
- const HCFChoice *A = hte->key;
+ // add shift entries
+ for(HSlistNode *x = dfa->transitions->head; x; x = x->next) {
+ // for each transition x-A->y, add "shift, goto y" to table entry (x,A)
+ HLRTransition *t = x->elem;
- // iterate over the productions of A
- for(HCFSequence **p=A->seq; *p; p++) {
- // find all transitions marked by A
- // yields xAy -> rhs'
- // trace rhs starting in state x and following the transitions
+ HLRAction *action = shift_action(arena, t->to);
+ h_hashtable_put(table->rows[t->from], t->symbol, action);
+ }
+
+ // add reduce entries, record inadequate states
+ for(size_t i=0; i<dfa->nstates; i++) {
+ // find reducible items in state
+ H_FOREACH(dfa->states[i], HLRItem *item, void *v_)
+ if(item->mark == item->len) { // mark at the end
+ // XXX store more informative stuff in the inadeq records?
+ if(table->forall[i]) {
+ // reduce/reduce conflict with a previous item
+ h_slist_push(table->inadeq, (void *)(uintptr_t)i);
+ } else if(!h_hashtable_empty(table->rows[i])) {
+ // shift/reduce conflict with one of the row's entries
+ h_slist_push(table->inadeq, (void *)(uintptr_t)i);
+ } else {
+ // set reduce action for the entire row
+ table->forall[i] = reduce_action(arena, item->lhs, item->len);
+ }
}
+ H_END_FOREACH
+ }
+
+ return table;
+}
+
+
+
+/* LALR-via-SLR grammar transformation */
+
+static inline size_t seqsize(void *p_)
+{
+ size_t n=0;
+ for(void **p=p_; *p; p++) n++;
+ return n+1;
+}
+
+static size_t follow_transition(const HLRTable *table, size_t x, HCFChoice *A)
+{
+ HLRAction *action = h_hashtable_get(table->rows[x], A);
+ assert(action != NULL);
+ assert(action->type == HLR_SHIFT);
+ return action->nextstate;
+}
+
+static HCFChoice *transform_symbol(const HLRTable *table, HHashTable *map,
+ size_t x, HCFChoice *B, size_t z);
+
+static HCFChoice *transform_productions(const HLRTable *table, HHashTable *map,
+ size_t x, HCFChoice *xAy)
+{
+ HArena *arena = map->arena;
+
+ HCFSequence **seq = h_arena_malloc(arena, seqsize(xAy->seq)
+ * sizeof(HCFSequence *));
+ HCFSequence **p, **q;
+ for(p=xAy->seq, q=seq; *p; p++, q++) {
+ // trace rhs starting in state x and following the transitions
+ // xAy -> xBz ...
+
+ HCFChoice **B = (*p)->items;
+ HCFChoice **xBz = h_arena_malloc(arena, seqsize(B) * sizeof(HCFChoice *));
+ for(; *B; B++, xBz++) {
+ size_t z = follow_transition(table, x, *B);
+ *xBz = transform_symbol(table, map, x, *B, z);
+ x=z;
}
+ *xBz = NULL;
+
+ *q = h_arena_malloc(arena, sizeof(HCFSequence));
+ (*q)->items = xBz;
+ }
+ *q = NULL;
+ xAy->seq = seq;
+
+ return xAy; // pass-through
+}
+
+static inline HLRTransition *transition(HArena *arena,
+ size_t x, const HCFChoice *A, size_t y)
+{
+ HLRTransition *t = h_arena_malloc(arena, sizeof(HLRTransition));
+ t->from = x;
+ t->symbol = A;
+ t->to = y;
+ return t;
+}
+
+static HCFChoice *transform_symbol(const HLRTable *table, HHashTable *map,
+ size_t x, HCFChoice *B, size_t z)
+{
+ HArena *arena = map->arena;
+
+ // look up the transition in map, create symbol if not found
+ HLRTransition *x_B_z = transition(arena, x, B, z);
+ HCFChoice *xBz = h_hashtable_get(map, x_B_z);
+ if(!xBz) {
+ HCFChoice *xBz = h_arena_malloc(arena, sizeof(HCFChoice));
+ *xBz = *B;
+ h_hashtable_put(map, x_B_z, xBz);
}
- return gt;
+ return transform_productions(table, map, x, xBz);
+}
+
+static bool eq_transition(const void *p, const void *q)
+{
+ const HLRTransition *a=p, *b=q;
+ return (a->from == b->from && a->to == b->to && a->symbol == b->symbol);
+}
+
+static HHashValue hash_transition(const void *p)
+{
+ const HLRTransition *t = p;
+ return (h_hash_ptr(t->symbol) + t->from + t->to); // XXX ?
+}
+
+static HHashTable *enhance_grammar(const HCFGrammar *g, const HLRTable *tbl)
+{
+ HArena *arena = g->arena; // XXX ?
+ HHashTable *map = h_hashtable_new(arena, eq_transition, hash_transition);
+
+ // copy the start symbol over
+ HCFChoice *start = h_arena_malloc(arena, sizeof(HCFChoice));
+ *start = *(g->start);
+ h_hashtable_put(map, g->start, start);
+
+ transform_productions(tbl, map, 0, start);
+
+ return map;
+}
+
+
+
+/* LALR table generation */
+
+bool is_inadequate(HLRTable *table, size_t state)
+{
+ // XXX
+}
+
+bool has_conflicts(HLRTable *table)
+{
+ return !h_slist_empty(table->inadeq);
}
int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params)
{
// generate CFG from parser
- // construct LR(0) DFA
- // build parse table, shift-entries only
- // for each transition a--S-->b, add "shift, goto b" to table entry (a,S)
- // determine lookahead "by conversion to SLR"
- // transform grammar to encode transitions in symbols
- // -> lookahead for an item is the transformed left-hand side's follow set
- // finish table; for each state:
- // add reduce entries for its accepting items
- // in case of conflict, add lookahead info
+ // build LR(0) table
+ // if necessary, resolve conflicts "by conversion to SLR"
HCFGrammar *g = h_cfgrammar(mm__, parser);
if(g == NULL) // backend not suitable (language not context-free)
return -1;
- HLRDFA *dfa = h_lalr_dfa(g);
- if(dfa == NULL) // this should actually not happen
+ HLRTable *table = h_lr0_table(g);
+ if(table == NULL) // this should normally not happen
return -1;
- // create table with shift actions
- HLRTable *table = h_lrtable_new(mm__, dfa->nstates);
- for(HSlistNode *x = dfa->transitions->head; x; x = x->next) {
- HLRTransition *t = x->elem;
- HLRAction *action = h_arena_malloc(table->arena, sizeof(HLRAction));
- action->type = HLR_SHIFT;
- action->nextstate = t->to;
- h_hashtable_put(table->rows[t->from], t->symbol, action);
+ if(has_conflicts(table)) {
+ HHashTable *map = enhance_grammar(g, table);
+ if(map == NULL) // this should normally not happen
+ return -1;
+
+ // XXX resolve conflicts
+ // iterate over dfa's transitions where 'from' state is inadequate
+ // look up enhanced symbol corr. to the transition
+ // for each terminal in follow set of enh. symbol:
+ // put reduce action into table cell (state, terminal)
+ // conflict if already occupied
}
- // mapping (state,item)-pairs to the symbols of the new grammar
- HHashTable **syms = h_arena_malloc(g->arena, dfa->nstates * sizeof(HHashTable *));
- // XXX use a different arena for this (and other things)
-
- HCFGrammar *gt = transform_grammar(g, table, dfa, syms);
- if(gt == NULL) // this should actually not happen
- return -1;
-
- // XXX fill in reduce actions
-
- return 0;
+ h_cfgrammar_free(g);
+ parser->backend_data = table;
+ return has_conflicts(table)? -1 : 0;
}
void h_lalr_free(HParser *parser)
{
- // XXX free data structures
+ HLRTable *table = parser->backend_data;
+ h_lrtable_free(table);
parser->backend_data = NULL;
parser->backend = PB_PACKRAT;
}
@@ -538,7 +702,7 @@ int test_lalr(void)
h_pprint_grammar(stdout, g, 0);
printf("\n==== D F A ====\n");
- HLRDFA *dfa = h_lalr_dfa(g);
+ HLRDFA *dfa = h_lr0_dfa(g);
if(dfa)
h_pprint_lrdfa(stdout, g, dfa, 0);
else
--
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