yacc.c: initialize yylval and yylloc.

[bison.git] / src / tables.h

diff --git a/src/tables.h b/src/tables.h
index b21fa7b0b0079520ee130bec35339d440c4bd749..8b5c1fa4c285d54c74879cf5b5db478913c0a845 100644 (file)
--- a/src/tables.h
+++ b/src/tables.h
@@ -1,5 +1,6 @@
 /* Prepare the LALR and GLR parser tables.
-   Copyright (C) 2002, 2004, 2009 Free Software Foundation, Inc.
+
+   Copyright (C) 2002, 2004, 2009-2012 Free Software Foundation, Inc.
 
    This file is part of Bison, the GNU Compiler Compiler.
 
@@ -45,6 +46,24 @@
 
    YYSTOS[S] = the symbol number of the symbol that leads to state S.
 
+   YYFINAL = the state number of the termination state.
+
+   YYTABLE = a vector filled with portions for different uses, found
+   via YYPACT and YYPGOTO, described below.
+
+   YYLAST ( = high) the number of the last element of YYTABLE, i.e.,
+   sizeof (YYTABLE) - 1.
+
+   YYCHECK = a vector indexed in parallel with YYTABLE.  It indicates,
+   in a roundabout way, the bounds of the portion you are trying to
+   examine.
+
+   Suppose that the portion of YYTABLE starts at index P and the index
+   to be examined within the portion is I.  Then if YYCHECK[P+I] != I,
+   I is outside the bounds of what is actually allocated, and the
+   default (from YYDEFACT or YYDEFGOTO) should be used.  Otherwise,
+   YYTABLE[P+I] should be used.
+
    YYDEFACT[S] = default reduction number in state s.  Performed when
    YYTABLE doesn't specify something else to do.  Zero means the default
    is an error.
@@ -58,10 +77,10 @@
    YYTABLE to find out what action to perform.
 
    If YYPACT[S] == YYPACT_NINF, if YYPACT[S] + I is outside the bounds
-   of YYTABLE (from 0 to YYLAST), or if YYCHECK indicates that I is
-   outside the bounds of the portion for S, then the default action
-   (from YYDEFACT and YYDEFGOTO) should be used instead of YYTABLE.
-   Otherwise, the value YYTABLE[YYPACT[S] + I] should be used even if
+   of YYTABLE (from 0 to YYLAST), or I is outside the bounds for portion
+   S (that is, YYCHECK[YYPACT[S] + I] != I), then the default action
+   (that is, YYDEFACT[S]) should be used instead of YYTABLE.  Otherwise,
+   the value YYTABLE[YYPACT[S] + I] should be used even if
    YYPACT[S] < 0.
 
    If the value in YYTABLE is positive, we shift the token and go to
@@ -69,33 +88,29 @@
 
    If the value is negative, it is minus a rule number to reduce by.
 
-   If the value is zero, the default action from YYDEFACT[S] is used.
-
    If the value is YYTABLE_NINF, it's a syntax error.
 
    YYPGOTO[I] = the index in YYTABLE of the portion describing what to
    do after reducing a rule that derives variable I + NTOKENS.  This
    portion is indexed by the parser state number, S, as of before the
-   text for this nonterminal was read.  The value from YYTABLE is the
-   state to go to if the corresponding value in YYCHECK is S.
-
-   YYTABLE = a vector filled with portions for different uses, found
-   via YYPACT and YYPGOTO.
-
-   YYCHECK = a vector indexed in parallel with YYTABLE.  It indicates,
-   in a roundabout way, the bounds of the portion you are trying to
-   examine.
-
-   Suppose that the portion of YYTABLE starts at index P and the index
-   to be examined within the portion is I.  Then if YYCHECK[P+I] != I,
-   I is outside the bounds of what is actually allocated, and the
-   default (from YYDEFACT or YYDEFGOTO) should be used.  Otherwise,
-   YYTABLE[P+I] should be used.
-
-   YYFINAL = the state number of the termination state.
-
-   YYLAST ( = high) the number of the last element of YYTABLE, i.e.,
-   sizeof (YYTABLE) - 1.  */
+   text for this nonterminal was read.
+
+   If YYPGOTO[I] + S is outside the bounds of YYTABLE (from 0 to YYLAST)
+   or if S is outside the bounds of the portion for I (that is,
+   YYCHECK[YYPGOTO[I] + S] != S), then the default state (that is,
+   YYDEFGOTO[I]) should be used instead of YYTABLE.  Otherwise,
+   YYTABLE[YYPGOTO[I] + S] is the state to go to even if YYPGOTO[I] < 0.
+
+   When the above YYPACT, YYPGOTO, and YYCHECK tests determine that a
+   value from YYTABLE should be used, that value is never zero, so it is
+   useless to check for zero.  When those tests indicate that the value
+   from YYDEFACT or YYDEFGOTO should be used instead, the value from
+   YYTABLE *might* be zero, which, as a consequence of the way in which
+   the tables are constructed, also happens to indicate that YYDEFACT or
+   YYDEFGOTO should be used.  However, the YYTABLE value cannot be
+   trusted when the YYDEFACT or YYDEFGOTO value should be used.  In
+   summary, forget about zero values in YYTABLE.
+*/
 
 extern int nvectors;