There's some documentation on this in the User's Guide: http://www.haskell.org/ghc/docs/latest/html/users_guide/x1075.html#GHCI- DEFAULTING Cheers, Simon On 23 August 2004 17:15, Simon Peyton-Jones wrote:
The binding let t = printQ falls under the monomorphism restriction. The Haskell Report would not default (Show a), so you might think you'd get an "ambiguous type variable" error. But it's so annoying to get this error for ghci> show [] that GHCi is a bit more eager about defaulting ambiguous types: it'll apply defaulting if all the constrained classes are standard, and at least one of them is numeric *or* is Show, Eq or Ord. The *or* part is the non-standard bit.
Admittedly, I'm not sure this is documented.
Simon
-----Original Message----- From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- bounces@haskell.org] On Behalf Of Abraham Egnor Sent: 23 August 2004 16:02 To: glasgow-haskell-users@haskell.org Subject: overzealous defaulting?
I'm not sure if this is an actual bug, as opposed to an odd instance of defaulting:
*GUI.Parser> let printQ q = runQ q >>= print *GUI.Parser> :t printQ printQ :: forall a. (Show a) => Q a -> IO () *GUI.Parser> let p = printQ *GUI.Parser> :t p p :: Q Integer -> IO ()
...but I'm not sure when that would ever be the correct behavior.
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