+# AT_CALC_PUSHDEFS($1, $2, [BISON-OPTIONS])
+# -----------------------------------------
+# This macro works around the impossibility to define macros
+# inside macros, because issuing `[$1]' is not possible in M4 :(.
+# This sucks hard, GNU M4 should really provide M5 like $$1.
+m4_define([AT_CHECK_PUSHDEFS],
+[m4_if([$1$2], $[1]$[2], [],
+ [m4_fatal([$0: Invalid arguments: $@])])dnl
+m4_pushdef([AT_PARAM_IF],
+[m4_bmatch([$3], [%parse-param], [$1], [$2])])
+m4_pushdef([AT_LOCATION_IF],
+[m4_bmatch([$3], [%locations], [$1], [$2])])
+m4_pushdef([AT_PURE_IF],
+[m4_bmatch([$3], [%pure-parser], [$1], [$2])])
+m4_pushdef([AT_GLR_IF],
+[m4_bmatch([$3], [%glr-parser], [$1], [$2])])
+m4_pushdef([AT_PURE_AND_LOC_IF],
+[m4_bmatch([$3], [%locations.*%pure-parser\|%pure-parser.*%locations],
+ [$1], [$2])])
+m4_pushdef([AT_GLR_OR_PARAM_IF],
+[m4_bmatch([$3], [%glr-parser\|%parse-param], [$1], [$2])])
+
+# yyerror receives the location if %location & %pure & (%glr or %parse-param).
+m4_pushdef([AT_YYERROR_ARG_LOC_IF],
+[AT_GLR_OR_PARAM_IF([AT_PURE_AND_LOC_IF([$1], [$2])],
+ [$2])])
+# yyerror cannot see the locations if !glr & pure & !param.
+m4_pushdef([AT_YYERROR_SEES_LOC_IF],
+[AT_LOCATION_IF([AT_GLR_IF([$1],
+ [AT_PURE_IF([AT_PARAM_IF([$1], [$2])],
+ [$1])])],
+ [$2])])