[Haskell-beginners] Is this a GHC bug? Problem inferring type

[Peter Hall]

Ah, thanks for the explanation. I hadn't heard of ExtendedDefaultRules
before.

Peter


On 8 June 2013 14:35, Brandon Allbery <allbery.b at gmail.com> wrote:

> On Sat, Jun 8, 2013 at 9:02 AM, Peter Hall <peter.hall at memorphic.com>wrote:
>
>> This is confusing me, and I'm wondering if it's a compiler bug. I have
>> this:
>>
>>    foo = (++) `on` show
>>
>> I'm expecting the type to be:
>>
>>     foo :: Show a => a -> a -> String
>>
>> But GHCI is inferring:
>>
>>     foo :: () -> () -> String
>>
>
>  No bug; it's the monomorphism restriction combining with extended
> defaulting to infer a monomorphic type. If you want to keep the
> monomorphism restriction and throw a type error, disable
> ExtendedDefaultRules.
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
>
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