Error message should suggest UnboxedTuples language extension

[tim]

If I compile this code:

module Foo where
import GHC.Integer

foo x y =
   case x `quotRemInteger` y of
    (# y, z #) -> 42

I get:

foo.hs:7:5: Parse error in pattern

It would be better if the error message suggested using -XUnboxedTuples.

[simonpj]

It would be better, yes. And usually I'm very keen to improve error messages.

The reason we don't is that -XUnboxedTuples tells the lexical analyser to recognise the lexemes (# and #). The idea is not to interfere with Haskell 98 when the extension is switched off.

For example (# 3) is a section in H98. So just seeing (# isn't enough to say "I suggest you use -XUnboxedTuples".

So that's why it's tricky. I can't see an easy way to give you want you ask.

Simon