From e346210c038bc5c6ab2aca99e04f8452181406e1 Mon Sep 17 00:00:00 2001
From: Akim Demaille <akim.demaille@gmail.com>
Date: Sun, 27 Jan 2019 18:29:17 +0100
Subject: [PATCH] add LR(0) output

This should not be used to generate parsers.  My point is actually to
facilitate debugging (when tweaking the generation of the LR(0)
automaton for instance, not carying -yet- about lookaheads).

* src/reader.c (prepare_percent_define_front_end_variables): Add lr(0).
* src/conflicts.c (set_conflicts): Be robust to reds not having
lookaheads at all.
* src/ielr.c (LrType, lr_type_get): Adjust.
(ielr): Implement support for LR(0).
* src/lalr.c (lalr_free): Don't free LA when it's not computed.
---
 src/conflicts.c | 17 +++++-----
 src/ielr.c      | 82 +++++++++++++++++++++++++++++++------------------
 src/reader.c    | 11 ++++---
 3 files changed, 68 insertions(+), 42 deletions(-)

diff --git a/src/conflicts.c b/src/conflicts.c
index c849e898..734b8c15 100644
--- a/src/conflicts.c
+++ b/src/conflicts.c
@@ -369,13 +369,16 @@ set_conflicts (state *s, symbol **errors)
     s->solved_conflicts_xml = obstack_finish0 (&solved_conflicts_xml_obstack);
 
   /* Loop over all rules which require lookahead in this state.  Check
-     for conflicts not resolved above.  */
-  for (int i = 0; i < reds->num; ++i)
-    {
-      if (!bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
-        conflicts[s->number] = 1;
-      bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
-    }
+     for conflicts not resolved above.
+
+     reds->lookahead_tokens can be NULL if the LR type is LR(0).  */
+  if (reds->lookahead_tokens)
+    for (int i = 0; i < reds->num; ++i)
+      {
+        if (!bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
+          conflicts[s->number] = 1;
+        bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
+      }
 }
 
 
diff --git a/src/ielr.c b/src/ielr.c
index fe1217b1..47ce38c3 100644
--- a/src/ielr.c
+++ b/src/ielr.c
@@ -36,7 +36,36 @@
 #include "symtab.h"
 
 /** Records the value of the \%define variable lr.type.  */
-typedef enum { LR_TYPE__LALR, LR_TYPE__IELR, LR_TYPE__CANONICAL_LR } LrType;
+typedef enum
+  {
+   LR_TYPE__LR0,
+   LR_TYPE__LALR,
+   LR_TYPE__IELR,
+   LR_TYPE__CANONICAL_LR
+  } LrType;
+
+/* The user's requested LR type.  */
+static LrType
+lr_type_get (void)
+{
+  char *type = muscle_percent_define_get ("lr.type");
+  LrType res;
+  if (STREQ (type, "lr(0)"))
+    res = LR_TYPE__LR0;
+  else if (STREQ (type, "lalr"))
+    res = LR_TYPE__LALR;
+  else if (STREQ (type, "ielr"))
+    res = LR_TYPE__IELR;
+  else if (STREQ (type, "canonical-lr"))
+    res = LR_TYPE__CANONICAL_LR;
+  else
+    {
+      aver (false);
+      abort ();
+    }
+  free (type);
+  return res;
+}
 
 /**
  * \post:
@@ -1052,46 +1081,39 @@ ielr_split_states (bitsetv follow_kernel_items, bitsetv always_follows,
 }
 
 
-/* The user's requested LR type.  */
-static LrType
-lr_type_get (void)
-{
-  char *type = muscle_percent_define_get ("lr.type");
-  LrType res;
-  if (STREQ (type, "lalr"))
-    res = LR_TYPE__LALR;
-  else if (STREQ (type, "ielr"))
-    res = LR_TYPE__IELR;
-  else if (STREQ (type, "canonical-lr"))
-    res = LR_TYPE__CANONICAL_LR;
-  else
-    {
-      aver (false);
-      abort ();
-    }
-  free (type);
-  return res;
-}
-
-
 void
 ielr (void)
 {
   LrType lr_type = lr_type_get ();
 
   /* Phase 0: LALR(1).  */
-  timevar_push (tv_lalr);
-  if (lr_type == LR_TYPE__CANONICAL_LR)
-    set_goto_map ();
-  else
-    lalr ();
-  if (lr_type == LR_TYPE__LALR)
+  switch (lr_type)
     {
+    case LR_TYPE__LR0:
+      timevar_push (tv_lalr);
+      set_goto_map ();
+      timevar_pop (tv_lalr);
+      return;
+
+    case LR_TYPE__CANONICAL_LR:
+      timevar_push (tv_lalr);
+      set_goto_map ();
+      timevar_pop (tv_lalr);
+      break;
+
+    case LR_TYPE__LALR:
+      timevar_push (tv_lalr);
+      lalr ();
       bitsetv_free (goto_follows);
       timevar_pop (tv_lalr);
       return;
+
+    case LR_TYPE__IELR:
+      timevar_push (tv_lalr);
+      lalr ();
+      timevar_pop (tv_lalr);
+      break;
     }
-  timevar_pop (tv_lalr);
 
   {
     bitsetv follow_kernel_items;
diff --git a/src/reader.c b/src/reader.c
index 075d6c7a..dbc834a4 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -754,11 +754,12 @@ prepare_percent_define_front_end_variables (void)
 
   /* Check %define front-end variables.  */
   {
-    static char const * const values[] = {
-      "lr.type", "lalr", "ielr", "canonical-lr", NULL,
-      "lr.default-reduction", "most", "consistent", "accepting", NULL,
-      NULL
-    };
+    static char const * const values[] =
+      {
+       "lr.type", "lr(0)", "lalr", "ielr", "canonical-lr", NULL,
+       "lr.default-reduction", "most", "consistent", "accepting", NULL,
+       NULL
+      };
     muscle_percent_define_check_values (values);
   }
 }