ghci obscurity

[Simon Peyton-Jones]

That's strange, if you are using the HEAD.  I get

Prelude Data.Generics> (\x -> case cast x of Just x'@(a,b) -> print x';
Nothing -> putStrLn "No match") (2::Int,3::Int)
No match

Incidentally, the 'no match' is because you aren't fixing the type of
'a' and 'b', so they are ambiguous and are defaulted to
(Integer,Integer). 

Simon

| -----Original Message-----
| From: glasgow-haskell-bugs-bounces at haskell.org
[mailto:glasgow-haskell-bugs-
| bounces at haskell.org] On Behalf Of Frederik Eaton
| Sent: 24 May 2005 10:19
| To: Simon Peyton-Jones
| Cc: glasgow-haskell-bugs at haskell.org
| Subject: Re: ghci obscurity
| 
| Thank you!
| 
| I imagine that if you think you've fixed it then you have, but here's
| an example:
| 
| Prelude Data.Generics> (\x -> case cast x of Just x'@(a,b) -> print
x'; Nothing -> putStrLn "No
| match") (2::Int,3::Int)
| 
| Top level:
|     No instance for (Show (IO ()))
|       arising from use of `print' at Top level
|     Probable fix: add an instance declaration for (Show (IO ()))
|     In a 'do' expression: print it
| 
| I think the real error is that (,) is missing an instance...
| 
| Frederik