+ -- code type notation extension
+ | '<[' incdepth exp decdepth ']>' { sL (comb2 $3 $>) (HsHetMetBrak placeHolderType $3) }
+ | '~~' decdepth aexp incdepth { sL (comb2 $3 $>) (HsHetMetEsc placeHolderType placeHolderType $3) }
+ | '%%' decdepth aexp incdepth { sL (comb2 $3 $>) (HsHetMetCSP placeHolderType $3) }
+