H_VALIDATE_APPLY macro

I've found this especially useful in combination with my own
_attr_uint_const for things like flags and type specifiers.

It's possible that its usefulness might be diminished significantly if
there were a built-in bitfield constant parser -- that certainly would
eliminate all of my current uses of it -- but it still seems nicely
symmetric with H_ACT_APPLY.

src/glue.h

@@ -11,7 +11,8 @@
 //
 // A few standard semantic actions are defined below. The H_ACT_APPLY macro
 // allows semantic actions to be defined by "partial application" of
-// a generic action to fixed paramters.
+// a generic action to fixed paramters. H_VALIDATE_APPLY is similar for
+// h_atter_bool.
 //
 // The definition of more complex semantic actions will usually consist of
 // extracting data from the given parse tree and constructing a token of custom
@@ -113,6 +114,12 @@ HParsedToken *h_act_ignore(const HParseResult *p, void* user_data);
     return paction(__VA_ARGS__, p, user_data);                          \
   }
 
+// Similar, but for validations.
+#define H_VALIDATE_APPLY(myvalidation, pvalidation, ...)  \
+  bool myvalidation(HParseResult* p, void* user_data) {   \
+    return pvalidation(__VA_ARGS__, p, user_data);        \
+  }
+
 
 //
 // Working with HParsedTokens