GHCi does not find instances
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: nhn@cs.nott.ac.uk
Trac metadata
Trac field |
Value |
Version |
6.4 |
Type |
Bug |
TypeOfFailure |
OtherFailure |
Priority |
normal |
Resolution |
ResolvedFixed |
Component |
Compiler |
Test case |
|
Differential revisions |
|
BlockedBy |
|
Related |
|
Blocking |
|
CC |
|
Operating system |
|
Architecture |
|