Simon Peyton-Jones wrote:
| > arbitrarySeq :: Sequence a -> Gen RepSeqVal | > arbitrarySeq Nil = | > return (RepSeqVal Nil Empty) | > arbitrarySeq (Cons (CTMandatory (NamedType n i t)) ts) = | > do u <- arbitraryType t | > us <- arbitrarySeq ts | > case u of | > RepTypeVal a v -> | > case us of | > RepSeqVal bs vs -> | > return (RepSeqVal (Cons (CTMandatory (NamedType n i a)) bs) (v:*:vs)) | | | > QuickTest.lhs:240:13: | > GADT pattern match in non-rigid context for `Nil' | > Solution: add a type signature | > In the pattern: Nil | > In the definition of `arbitrarySeq': | > arbitrarySeq Nil = return (RepSeqVal Nil Empty)
That looks odd to me. But it's hard to help without having the code. If you send it I'll try to help.
| > Did you try giving a type signature to the (entire) case expression, | > as I suggested? That should do it. | > | | I'm not sure what this means or how to do it. Can you give an example or | is it buried in some earlier email? I will go and have another look.
I mean replace (case blah of { ... }) by (case blah of { ... }) :: type-sig
That is, attach a type signature to the case expression itself. Does that help at least explain what the sentence means? If so would you like to clarify the wiki advice?
Thanks
Simon
Simon, I'm sorry to have put you to so much trouble by accidentally using an old version of ghc I must have had lying around. As penance, I will go and update the wiki with what I have learnt. Dominic.