[Haskell-cafe] type class constraints headache

[Miguel Mitrofanov]

Which "a" should it use for "methods"?


On 4 Mar 2010, at 09:07, muneson wrote:

>
> When writing a command-line interface I ran into type class conflicts
> I don't understand. Could anyone explain why ghc 6.10.4 compiles this
>
>> methods :: (Eq a) => [(String, a)]
>> methods =
>>  [ ("method1", undefined )
>>  , ("method2", undefined)
>>  ]
>
>
> but not the following?
>
>> methods :: (Eq a) => [(String, a)]
>> methods =
>>  [ ("method1", undefined )
>>  , ("method2", undefined)
>>  ]
>>
>> enumerateMethodNames :: [String]
>> enumerateMethodNames = map fst methods
>
>
> thanks,
>
> Marcus
>
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