add h_left, h_right, h_middle combinators

src/parsers/ignoreseq.c

@@ -0,0 +1,73 @@
+#include "parser_internal.h"
+
+
+//
+// general case: parse sequence, pick one result
+//
+
+typedef struct {
+  const HParser **parsers;
+  size_t count;         // how many parsers in 'ps'
+  size_t which;         // whose result to return
+} HIgnoreSeq;
+
+static HParseResult* parse_ignoreseq(void* env, HParseState *state) {
+  const HIgnoreSeq *seq = (HIgnoreSeq*)env;
+  HParseResult *res = NULL;
+
+  for (size_t i=0; i < seq->count; ++i) {
+    HParseResult *tmp = h_do_parse(seq->parsers[i], state);
+    if (!tmp)
+      return NULL;
+    else if (i == seq->which)
+      res = tmp;
+  }
+
+  return res;
+}
+
+static const HParserVtable ignoreseq_vt = {
+  .parse = parse_ignoreseq,
+};
+
+
+//
+// API frontends
+//
+
+static const HParser* h_leftright(const HParser* p, const HParser* q, size_t which) {
+  HIgnoreSeq *seq = g_new(HIgnoreSeq, 1);
+  seq->parsers = g_new(const HParser*, 2);
+  seq->parsers[0] = p;
+  seq->parsers[1] = q;
+  seq->count = 2;
+  seq->which = which;
+
+  HParser *ret = g_new(HParser, 1);
+  ret->vtable = &ignoreseq_vt;
+  ret->env = (void*)seq;
+  return ret;
+}
+
+const HParser* h_left(const HParser* p, const HParser* q) {
+  return h_leftright(p, q, 0);
+}
+
+const HParser* h_right(const HParser* p, const HParser* q) {
+  return h_leftright(p, q, 1);
+}
+
+const HParser* h_middle(const HParser* p, const HParser* x, const HParser* q) {
+  HIgnoreSeq *seq = g_new(HIgnoreSeq, 1);
+  seq->parsers = g_new(const HParser*, 3);
+  seq->parsers[0] = p;
+  seq->parsers[1] = x;
+  seq->parsers[2] = q;
+  seq->count = 3;
+  seq->which = 1;
+
+  HParser *ret = g_new(HParser, 1);
+  ret->vtable = &ignoreseq_vt;
+  ret->env = (void*)seq;
+  return ret;
+}