Bit of a simple question but I'm struggling to find information on this via Google. I have a sum type, when the input is type A I want to process it, when it is type B I want to return MyError "Expected type A but actually got type B". However I also have C,D,E,F, etc which should also return similar errors so don't want to hardcode this string. Is there a function I can call on a variable to get the name of the data constructor that created it? I could create a typeName function but I want to avoid boiler plate if I can. For reference what I'm actually doing is parsing Java class files. The constant pool I've represented as a map of a sum ConstantPoolEntry type (the Java constant pool for some reason skips an index on some types so can't be a simple list). Certain Java class file entries have a reference to the constant pool that must be of a specific constant type so I want to report badly formed entries to the user. Thanks, Gareth