GHCi does not find instances
|Reported by:||nobody||Owned by:||nobody|
|Type of failure:||Test Case:|
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This report concerns GHC HEAD (6.3) as downloaded from CVS around 2PM on 20 Jan 2005. It seems GHCi does not find some instance declarations. Consider the following trivial example: module Foo where data Foo = Foo instance Show Foo where show Foo = "Foo" When loaded into GHCi, regardless of whether it is first compiled or not, GHCi claims that Foo is not an instance of Show. E.g. Prelude> :load Foo Compiling Foo ( Foo.hs, interpreted ) Ok, modules loaded: Foo. *Foo> show Foo <interactive>:1:0: No instance for (Show Foo) arising from use of `show' at <interactive>:1:0-3 Probable fix: add an instance declaration for (Show Foo) In the definition of `it': it = show Foo *Foo> :i Foo data Foo = Foo -- Defined at Foo.hs:3:5 But Foo is plainly an instance of Show. GHC itself has no problems with this (of course). Best, /Henrik e-mail: firstname.lastname@example.org
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