add grammar representation functions and WIP LL scaffold

src/backends/ll.c

@@ -2,15 +2,153 @@
 #include "../internal.h"
 #include "../parsers/parser_internal.h"
 
+#define H_LL_END_TOKEN 256
 
-int h_ll_compile(HAllocator* mm__, const HParser* parser, const void* params) {
+
-  return -1; // TODO
+/* Grammar representation and analysis */
+
+typedef struct HCFGrammar_ {
+  HHashSet    *nts;     // HCFChoices, each representing the alternative
+                        // productions for one nonterminal
+  HHashSet    *geneps;  // set of NTs that can generate the empty string
+  HHashTable  *first;   // "first" sets of the grammar's nonterminals
+  HArena      *arena;
+} HCFGrammar;
+
+bool h_eq_pointer(const void *p, const void *q) { return (p==q); }
+HHashValue h_hash_ptr(const void *p) { return (uintptr_t)p; }
+
+HCFGrammar *h_grammar_new(HAllocator *mm__)
+{
+  HCFGrammar *g = h_new(HCFGrammar, 1);
+  assert(g != NULL);
+
+  g->arena  = h_new_arena(mm__, 0);     // default blocksize
+  g->nts    = h_hashset_new(g->arena, h_eq_pointer, h_hash_ptr);
+  g->geneps = NULL;
+  g->first  = NULL;
+
+  return g;
 }
 
-HParseResult *h_ll_parse(HAllocator* mm__, const HParser* parser, HParseState* parse_state) {
+void h_grammar_collect(HCFGrammar *grammar, HCFChoice *symbol); // helper
+
+/* Convert 'parser' into CFG representation by desugaring and compiling the set
+ * of nonterminals.
+ * A NULL return means we are unable to represent the parser as a CFG.
+ */
+HCFGrammar *h_grammar(HAllocator* mm__, const HParser *parser)
+{
+  // convert parser to CFG form ("desugar").
+  HCFChoice *desugared = h_desugar(mm__, parser);
+  if(desugared == NULL)
+    return NULL;  // -> backend not suitable for this parser
+
+  HCFGrammar *g = h_grammar_new(mm__);
+
+  // recursively traverse the desugared form and collect all HCFChoices that
+  // represent a nonterminal.
+  h_grammar_collect(g, desugared);
+
+  if(h_hashset_empty(g->nts)) {
+    // desugared is a single nonterminal. wrap it.
+    // XXX is this even necessary?
+  }
+
+  return g;
+}
+
+/* Add all nonterminals reachable from symbol to grammar. */
+void h_grammar_collect(HCFGrammar *grammar, HCFChoice *symbol)
+{
+  HCFSequence **s;  // for the rhs (sentential form) of a production
+  HCFChoice **x;    // for a symbol in s
+
+  if(h_hashset_present(grammar->nts, symbol))
+    return;     // already visited, get out
+
+  switch(symbol->type) {
+  case HCF_CHAR:
+  case HCF_END:
+    break;  // it's a terminal symbol, nothing to do
+
+  case HCF_CHARSET:
+    h_hashset_put(grammar->nts, symbol);
+    break;  // this type has only terminal children
+
+  case HCF_CHOICE:
+    h_hashset_put(grammar->nts, symbol);
+    // each element s of symbol->seq (HCFSequence) represents the RHS of
+    // a production. call self on all symbols (HCFChoice) in s.
+    for(s = symbol->seq; *s != NULL; s++) {
+      for(x = (*s)->items; *x != NULL; x++) {
+        h_grammar_collect(grammar, *x);
+      }
+    }
+    break;
+
+  default:
+    assert_message(0, "unknown HCFChoice type");
+  }
+}
+
+// first_set(grammar?, production)
+// follow_set
+
+
+
+/* LL parse table and associated data */
+
+typedef struct HLLTable_ {
+  unsigned int **arr;             // Nonterminals numbered from 1, 0 = error.
+} HLLTable;
+
+typedef struct HLLData_ {
+  HCFGrammar *grammar;
+  HLLTable *table;
+} HLLData;
+
+#if 0
+/* Interface to look up an entry in the parse table. */
+unsigned int h_ll_lookup(const HLLTable *table, unsigned int nonterminal, uint8_t token)
+{
+  assert(nonterminal > 0);
+  return table->arr[n*257+token];
+}
+#endif
+
+// XXX predict_set
+
+int h_ll_compile(HAllocator* mm__, const HParser* parser, const void* params)
+{
+  // Convert parser to a CFG. This can fail as indicated by a NULL return.
+  HCFGrammar *grammar = h_grammar(mm__, parser);
+  if(grammar == NULL)
+    return -1;                  // -> Backend unsuitable for this parser.
+
+  // TODO: eliminate common prefixes
+  // TODO: eliminate left recursion
+  // TODO: avoid conflicts by splitting occurances?
+
+  // XXX generate table and store in parser->data.
+  // XXX any other data structures needed?
+
+  return -1; // XXX 0 on success
+}
+
+
+
+/* LL driver */
+
+HParseResult *h_ll_parse(HAllocator* mm__, const HParser* parser, HParseState* parse_state)
+{
+  // get table from parser->data.
+  // run driver.
   return NULL; // TODO
 }
 
+
+
 HParserBackendVTable h__ll_backend_vtable = {
   .compile = h_ll_compile,
   .parse = h_ll_parse