16-default-rule.patch

[Akim Demaille]

Index: ChangeLog
from  Akim Demaille  <address@hidden>
        
        * src/print.c (state_default_rule_compute): New, extracted from...
        (print_reductions): here.
        Pessimize, but clarify the code.
        * tests/conflicts.at (Defaulted Conflicted Reduction): New.
        
Index: TODO
--- TODO Fri, 28 Jun 2002 21:50:19 +0200 akim
+++ TODO Sun, 30 Jun 2002 11:10:59 +0200 akim
@@ -3,6 +3,16 @@
 * URGENT: Documenting C++ output
 Write a first documentation for C++ output.
 
+* Report and GLR
+How would Paul like to display the conflicted actions?  In particular,
+what when two reductions are possible on a given lookahead, but one is
+part of $default.  Should we make the two reductions explicit, or just
+keep $default?  See the following point.
+
+* Report and Disabled Reductions
+See `tests/conflicts.at (Defaulted Conflicted Reduction)', and decide
+what we want to do.
+
 * value_components_used
 Was defined but not used: where was it coming from?  It can't be to
 check if %union is used, since the user is free to $<foo>n on her
@@ -16,7 +26,9 @@
 * documentation
 Explain $axiom (and maybe change its name: BTYacc names it `goal',
 byacc `$accept' probably based on AT&T Yacc, Meta `Start'...).
-Complete the glossary (item, axiom, ?).
+Complete the glossary (item, axiom, ?).  Should we also rename `$'?
+BYacc uses `$end'.  `$eof' is attracting, but after all we may be
+parsing a string, a stream etc.
 
 * Error messages
 Some are really funky.  For instance
@@ -26,11 +38,11 @@
 is really weird.  Revisit them all.
 
 * Report documentation
-Extend with error.  The hard part will probably be finding the right
-rule so that a single state does not exhibit to many yet undocumented
-``features''.  Maybe an empty action ought to be presented too.  Shall
-we try to make a single grammar with all these features, or should we
-have several very small grammars?
+Extend with error productions.  The hard part will probably be finding
+the right rule so that a single state does not exhibit too many yet
+undocumented ``features''.  Maybe an empty action ought to be
+presented too.  Shall we try to make a single grammar with all these
+features, or should we have several very small grammars?
 
 * Documentation
 Some history of Bison and some bibliography would be most welcome.
Index: src/print.c
--- src/print.c Sat, 29 Jun 2002 21:11:31 +0200 akim
+++ src/print.c Sun, 30 Jun 2002 10:58:11 +0200 akim
@@ -165,138 +165,148 @@
     }
 }
 
-static void
-print_reductions (FILE *out, state_t *state)
+
+/*----------------------------------------------------------.
+| Return the default rule of this STATE if it has one, NULL |
+| otherwise.                                                |
+`----------------------------------------------------------*/
+
+static rule_t *
+state_default_rule_compute (state_t *state)
 {
-  int i;
-  shifts_t *shiftp = state->shifts;
   reductions_t *redp = state->reductions;
-  errs_t *errp = state->errs;
-  int nodefault = 0;
-
-  if (redp->nreds == 0)
-    return;
+  rule_t *default_rule = NULL;
+  int cmax = 0;
+  int i;
 
+  /* No need for a lookahead.  */
   if (state->consistent)
-    {
-      int rule = redp->rules[0];
-      symbol_number_t symbol = rules[rule].lhs->number;
-      fprintf (out, _("    $default\treduce using rule %d (%s)\n\n"),
-              rule - 1, symbol_tag_get (symbols[symbol]));
-      return;
-    }
+    return &rules[redp->rules[0]];
 
+  /* 1. Each reduction is possibly masked by the lookaheads on which
+     we shift (S/R conflicts)...  */
   bitset_zero (shiftset);
+  {
+    shifts_t *shiftp = state->shifts;
+    for (i = 0; i < shiftp->nshifts && SHIFT_IS_SHIFT (shiftp, i); i++)
+      if (!SHIFT_IS_DISABLED (shiftp, i))
+       {
+         /* If this state has a shift for the error token, don't use a
+            default rule.  */
+         if (SHIFT_IS_ERROR (shiftp, i))
+           return NULL;
+         bitset_set (shiftset, SHIFT_SYMBOL (shiftp, i));
+       }
+  }
 
-  for (i = 0; i < shiftp->nshifts && SHIFT_IS_SHIFT (shiftp, i); i++)
-    if (!SHIFT_IS_DISABLED (shiftp, i))
-      {
-       /* if this state has a shift for the error token, don't use a
-          default rule.  */
-       if (SHIFT_IS_ERROR (shiftp, i))
-         nodefault = 1;
-       bitset_set (shiftset, SHIFT_SYMBOL (shiftp, i));
-      }
-
-  for (i = 0; i < errp->nerrs; i++)
-    if (errp->errs[i])
-      bitset_set (shiftset, errp->errs[i]);
+  /* 2. Each reduction is possibly masked by the lookaheads on which
+     we raise an error (due to %nonassoc).  */
+  {
+    errs_t *errp = state->errs;
+    for (i = 0; i < errp->nerrs; i++)
+      if (errp->errs[i])
+       bitset_set (shiftset, errp->errs[i]);
+  }
 
-  if (state->nlookaheads == 1 && !nodefault)
+  for (i = 0; i < state->nlookaheads; ++i)
     {
-      rule_t *default_rule = state->lookaheads_rule[0];
+      int count = 0;
 
-      bitset_and (lookaheadset, state->lookaheads[0], shiftset);
+      /* How many non-masked lookaheads are there for this reduction?
+        */
+      bitset_andn (lookaheadset, state->lookaheads[i], shiftset);
+      count = bitset_count (lookaheadset);
 
-      BITSET_EXECUTE (lookaheadset, 0, i,
-      {
-       fprintf (out, _("    %-4s\t[reduce using rule %d (%s)]\n"),
-                symbol_tag_get (symbols[i]),
-                default_rule->number - 1,
-                symbol_tag_get_n (default_rule->lhs, 1));
-      });
-      fprintf (out, _("    $default\treduce using rule %d (%s)\n\n"),
-              default_rule->number - 1,
-              symbol_tag_get (default_rule->lhs));
+      if (count > cmax)
+       {
+         cmax = count;
+         default_rule = state->lookaheads_rule[i];
+       }
+
+      /* 3. And finally, each reduction is possibly masked by previous
+        reductions (in R/R conflicts, we keep the first reductions).
+        */
+      bitset_or (shiftset, shiftset, state->lookaheads[i]);
     }
-  else if (state->nlookaheads >= 1)
-    {
-      int cmax = 0;
-      int default_LA = -1;
-      rule_t *default_rule = NULL;
 
-      if (!nodefault)
-       for (i = 0; i < state->nlookaheads; ++i)
-         {
-           int count = 0;
+  return default_rule;
+}
 
-           bitset_andn (lookaheadset, state->lookaheads[i], shiftset);
-           count = bitset_count (lookaheadset);
 
-           if (count > cmax)
-             {
-               cmax = count;
-               default_LA = i;
-               default_rule = state->lookaheads_rule[i];
-             }
+/*----------------------------------------------------.
+| Report on OUT the reduction actions of this STATE.  |
+`----------------------------------------------------*/
 
-           bitset_or (shiftset, shiftset, lookaheadset);
-         }
+static void
+print_reductions (FILE *out, state_t *state)
+{
+  int i;
+  shifts_t *shiftp = state->shifts;
+  reductions_t *redp = state->reductions;
+  rule_t *default_rule = NULL;
 
-      bitset_zero (shiftset);
+  if (redp->nreds == 0)
+    return;
 
-      for (i = 0; i < shiftp->nshifts && SHIFT_IS_SHIFT (shiftp, i); i++)
-       if (!SHIFT_IS_DISABLED (shiftp, i))
-         bitset_set (shiftset, SHIFT_SYMBOL (shiftp, i));
+  default_rule = state_default_rule_compute (state);
 
-      for (i = 0; i < ntokens; i++)
-       {
-         int j;
-         int defaulted = 0;
-         int count = bitset_test (shiftset, i);
+  bitset_zero (shiftset);
+  for (i = 0; i < shiftp->nshifts && SHIFT_IS_SHIFT (shiftp, i); i++)
+    if (!SHIFT_IS_DISABLED (shiftp, i))
+      bitset_set (shiftset, SHIFT_SYMBOL (shiftp, i));
 
-         for (j = 0; j < state->nlookaheads; ++j)
-           if (bitset_test (state->lookaheads[j], i))
-             {
-               if (count == 0)
-                 {
-                   if (j != default_LA)
-                     fprintf (out,
-                              _("    %-4s\treduce using rule %d (%s)\n"),
-                              symbol_tag_get (symbols[i]),
-                              state->lookaheads_rule[j]->number - 1,
-                              symbol_tag_get_n 
(state->lookaheads_rule[j]->lhs, 1));
-                   else
-                     defaulted = 1;
+  for (i = 0; i < ntokens; i++)
+    {
+      int j;
+      int defaulted = 0;
+      int count = bitset_test (shiftset, i);
 
-                   count++;
-                 }
+      for (j = 0; j < state->nlookaheads; ++j)
+       if (bitset_test (state->lookaheads[j], i))
+         {
+           if (count == 0)
+             {
+               if (state->lookaheads_rule[j] != default_rule)
+                 fprintf (out,
+                          _("    %-4s\treduce using rule %d (%s)\n"),
+                          symbol_tag_get (symbols[i]),
+                          state->lookaheads_rule[j]->number - 1,
+                          symbol_tag_get_n (state->lookaheads_rule[j]->lhs, 
1));
                else
-                 {
-                   if (defaulted)
-                     fprintf (out,
-                              _("    %-4s\treduce using rule %d (%s)\n"),
-                              symbol_tag_get (symbols[i]),
-                              state->lookaheads_rule[default_LA]->number - 1,
-                              symbol_tag_get_n 
(state->lookaheads_rule[default_LA]->lhs, 1));
-                   defaulted = 0;
-                   fprintf (out,
-                            _("    %-4s\t[reduce using rule %d (%s)]\n"),
-                            symbol_tag_get (symbols[i]),
-                            state->lookaheads_rule[j]->number - 1,
-                            symbol_tag_get_n (state->lookaheads_rule[j]->lhs, 
1));
-                 }
+                 defaulted = 1;
+               count++;
              }
-       }
-
-      if (default_LA >= 0)
-       fprintf (out, _("    $default\treduce using rule %d (%s)\n"),
-                default_rule->number - 1,
-                symbol_tag_get (default_rule->lhs));
+           else
+             {
+               if (defaulted)
+                 fprintf (out,
+                          _("    %-4s\treduce using rule %d (%s)\n"),
+                          symbol_tag_get (symbols[i]),
+                          default_rule->number - 1,
+                          symbol_tag_get_n (default_rule->lhs, 1));
+               defaulted = 0;
+               fprintf (out,
+                        _("    %-4s\t[reduce using rule %d (%s)]\n"),
+                        symbol_tag_get (symbols[i]),
+                        state->lookaheads_rule[j]->number - 1,
+                        symbol_tag_get_n (state->lookaheads_rule[j]->lhs, 1));
+             }
+         }
     }
+
+  if (default_rule)
+    fprintf (out, _("    $default\treduce using rule %d (%s)\n"),
+            default_rule->number - 1,
+            symbol_tag_get (default_rule->lhs));
+  fputc ('\n', out);
 }
 
 
+/*--------------------------------------------------------------.
+| Report on OUT all the actions (shifts, gotos, reductions, and |
+| explicit erros from %nonassoc) of STATE.                      |
+`--------------------------------------------------------------*/
+
 static void
 print_actions (FILE *out, state_t *state)
 {
@@ -306,9 +316,9 @@
   if (shiftp->nshifts == 0 && redp->nreds == 0)
     {
       if (state->number == final_state->number)
-       fprintf (out, _("    $default\taccept\n"));
+       fprintf (out, _("    $default\taccept\n"));
       else
-       fprintf (out, _("    NO ACTIONS\n"));
+       fprintf (out, _("    NO ACTIONS\n"));
       return;
     }
 
@@ -317,6 +327,7 @@
   print_reductions (out, state);
   print_gotos (out, state);
 }
+
 
 static void
 print_state (FILE *out, state_t *state)
Index: tests/conflicts.at
--- tests/conflicts.at Sat, 15 Jun 2002 16:36:49 +0200 akim
+++ tests/conflicts.at Sun, 30 Jun 2002 11:03:05 +0200 akim
@@ -41,6 +41,7 @@ e: 'e' | /* Nothing. */;
 
 AT_CLEANUP
 
+
 ## ------------------- ##
 ## %nonassoc and eof.  ##
 ## ------------------- ##
@@ -237,26 +238,30 @@ exp: exp OP exp | NUM;
 AT_CLEANUP
 
 
-## --------------------- ##
-## Solved SR Conflicts.  ##
-## --------------------- ##
+## ------------------------- ##
+## Unresolved SR Conflicts.  ##
+## ------------------------- ##
 
-AT_SETUP([Solved SR Conflicts])
+AT_SETUP([Unresolved SR Conflicts])
 
 AT_KEYWORDS([report])
 
 AT_DATA([input.y],
 [[%token NUM OP
-%right OP
 %%
 exp: exp OP exp | NUM;
 ]])
 
-AT_CHECK([bison input.y -o input.c --report=all], 0, [], [])
+AT_CHECK([bison input.y -o input.c --report=all], 0, [],
+[input.y contains 1 shift/reduce conflict.
+])
 
 # Check the contents of the report.
 AT_CHECK([cat input.output], [],
-[[Grammar
+[[State 5 contains 1 shift/reduce conflict.
+
+
+Grammar
 
     0 $axiom: exp $
 
@@ -331,14 +336,154 @@ exp: exp OP exp | NUM;
 
 state 5
 
-    exp  ->  exp . OP exp  [$]   (rule 1)
-    exp  ->  exp OP exp .  [$]   (rule 1)
+    exp  ->  exp . OP exp  [$, OP]   (rule 1)
+    exp  ->  exp OP exp .  [$, OP]   (rule 1)
 
     OP         shift, and go to state 4
 
+    OP         [reduce using rule 1 (exp)]
     $default   reduce using rule 1 (exp)
 
-    Conflict between rule 2 and token OP resolved as reduce (%right OP).
+
+
+]])
+
+AT_CLEANUP
+
+
+
+## -------------------------------- ##
+## Defaulted Conflicted Reduction.  ##
+## -------------------------------- ##
+
+# When there are RR conflicts, some rules are disabled.  Usually it is
+# simply displayed as:
+#
+#    $           reduce using rule 3 (num)
+#    $           [reduce using rule 4 (id)]
+#
+# But when `reduce 3' is the default action, we'd produce:
+#
+#    $           [reduce using rule 4 (id)]
+#    $default    reduce using rule 3 (num)
+#
+# In this precise case (a reduction is masked by the default
+# reduction), we make the `reduce 3' explicit:
+#
+#    $           reduce using rule 3 (num)
+#    $           [reduce using rule 4 (id)]
+#    $default    reduce using rule 3 (num)
+#
+# Maybe that's not the best display, but then, please propose something
+# else.
+
+AT_SETUP([Defaulted Conflicted Reduction])
+AT_KEYWORDS([report])
+
+AT_DATA([input.y],
+[[%%
+exp: num | id;
+num: '0';
+id : '0';
+%%
+]])
+
+AT_CHECK([bison input.y -o input.c --report=all], 1, [],
+[input.y contains 1 reduce/reduce conflict.
+])
+
+# Check the contents of the report.
+AT_CHECK([cat input.output], [],
+[[State 1 contains 1 reduce/reduce conflict.
+
+
+Grammar
+
+    0 $axiom: exp $
+
+    1 exp: num
+    2    | id
+
+    3 num: '0'
+
+    4 id: '0'
+
+
+Terminals, with rules where they appear
+
+$ (0) 0
+'0' (48) 3 4
+error (256)
+
+
+Nonterminals, with rules where they appear
+
+$axiom (4)
+    on left: 0
+exp (5)
+    on left: 1 2, on right: 0
+num (6)
+    on left: 3, on right: 1
+id (7)
+    on left: 4, on right: 2
+
+
+state 0
+
+    $axiom  ->  . exp $   (rule 0)
+    exp  ->  . num   (rule 1)
+    exp  ->  . id   (rule 2)
+    num  ->  . '0'   (rule 3)
+    id  ->  . '0'   (rule 4)
+
+    '0'        shift, and go to state 1
+
+    exp        go to state 2
+    num        go to state 3
+    id         go to state 4
+
+
+
+state 1
+
+    num  ->  '0' .  [$]   (rule 3)
+    id  ->  '0' .  [$]   (rule 4)
+
+    $          reduce using rule 3 (num)
+    $          [reduce using rule 4 (id)]
+    $default   reduce using rule 3 (num)
+
+
+
+state 2
+
+    $axiom  ->  exp . $   (rule 0)
+
+    $          shift, and go to state 5
+
+
+
+state 3
+
+    exp  ->  num .   (rule 1)
+
+    $default   reduce using rule 1 (exp)
+
+
+
+state 4
+
+    exp  ->  id .   (rule 2)
+
+    $default   reduce using rule 2 (exp)
+
+
+
+state 5
+
+    $axiom  ->  exp $ .   (rule 0)
+
+    $default   accept
 
 
 ]])
@@ -381,7 +526,7 @@ exp: exp OP exp | NUM;
 exp: exp OP exp | NUM;
 ]])
 
-AT_CHECK([bison input.y -o input.c], 0)
+AT_CHECK([bison input.y -o input.c])
 AT_CLEANUP