-# b4_location_if(IF-TRUE, IF-FALSE)
-# ---------------------------------
-# Expand IF-TRUE, if locations are used, IF-FALSE otherwise.
-m4_define([b4_location_if],
-[m4_if(b4_locations_flag, [1],
- [$1],
- [$2])])
+
+# b4_define_flag_if(FLAG)
+# -----------------------
+# Define "b4_FLAG_if(IF-TRUE, IF-FALSE)" that depends on the
+# value of the Boolean FLAG.
+m4_define([b4_define_flag_if],
+[_b4_define_flag_if($[1], $[2], [$1])])
+
+# _b4_define_flag_if($1, $2, FLAG)
+# --------------------------------
+# 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([_b4_define_flag_if],
+[m4_if([$1$2], $[1]$[2], [],
+ [m4_fatal([$0: Invalid arguments: $@])])dnl
+m4_define([b4_$3_if],
+ [b4_flag_if([$3], [$1], [$2])])])
+
+
+# b4_FLAG_if(IF-TRUE, IF-FALSE)
+# -----------------------------
+# Expand IF-TRUE, if FLAG is true, IF-FALSE otherwise.
+b4_define_flag_if([defines]) # Whether headers are requested.
+b4_define_flag_if([error_verbose]) # Whether error are verbose.
+b4_define_flag_if([locations]) # Whether locations are tracked.
+b4_define_flag_if([pure]) # Whether the interface is pure.
+b4_define_flag_if([yacc]) # Whether POSIX Yacc is emulated.