+## ----------------- ##
+## Semantic Values. ##
+## ----------------- ##
+
+
+# b4_symbol_value(VAL, [TYPE])
+# ----------------------------
+# Given a semantic value VAL ($$, $1 etc.), extract its value of type
+# TYPE if TYPE is given, otherwise just return VAL. The result can be
+# used safetly, it is put in parens to avoid nasty precedence issues.
+# TYPE is *not* put in braces, provide some if needed.
+m4_define([b4_symbol_value],
+[($1[]m4_ifval([$2], [.$2]))])
+
+