Most of RVM desugaring done in first draft, for TQ to check.

src/parsers/ignoreseq.c

@@ -5,7 +5,7 @@
 // general case: parse sequence, pick one result
 //
 
-typedef struct {
+typedef struct HIgnoreSeq_ {
   const HParser **parsers;
   size_t len;         // how many parsers in 'ps'
   size_t which;         // whose result to return
@@ -44,10 +44,37 @@ static bool is_isValidCF(void *env) {
   return true;
 }
 
+static bool h_svm_action_ignoreseq(HArena *arena, HSVMContext *ctx, void* env) {
+  HIgnoreSeq *seq = (HIgnoreSeq*)env;
+  HParsedToken* save;
+  // We can assume that each subitem generated at most one item on the
+  // stack.
+  for (int i = seq->len - 1; i>=0; i--) {
+    if (i == seq->which && ctx->stack[ctx->stack_count]->token_type != TT_MARK) 
+      save = ctx->stack[ctx->stack_count-1];
+    // skip over everything up to and including the mark.
+    while (ctx->stack[--ctx->stack_count]->token_type != TT_MARK)
+      ;
+  }
+  ctx->stack[ctx->stack_count++] = save;
+}
+
+static bool is_ctrvm(HRVMProg *prog, void* env) {
+  HIgnoreSeq *seq = (HIgnoreSeq*)env;
+  for (size_t i=0; i<seq->len; ++i) {
+    h_rvm_insert_insn(prog, RVM_PUSH, 0);
+    if (!h_compile_regex(prog, seq->parsers[i]->env))
+      return false;
+  }
+  h_rvm_insert_insn(prog, RVM_ACTION, h_rvm_create_action(prog, h_svm_action_ignoreseq, env));
+  return true;
+}
+
 static const HParserVtable ignoreseq_vt = {
   .parse = parse_ignoreseq,
   .isValidRegular = is_isValidRegular,
   .isValidCF = is_isValidCF,
+  .compile_to_rvm = is_ctrvm,
 };