[Haskell] Proposal: Allow "\=" for field update in record update
robdockins at fastmail.fm
Fri Mar 4 09:50:36 EST 2005
> On Fri, 4 Mar 2005 15:26:52 +0100, Benjamin Franksen
> <benjamin.franksen at bessy.de> wrote:
>>On Sunday 20 February 2005 14:19, Keean Schupke wrote:
>>>TH has supported multi-parameter classes for a while... new in 6.4 is
>>>support for fundeps.
>>Yes, but unfortunately TH cannot create instances for them which is usually
>>the boilerplate you want to avoid. From Language.Haskell.TH:
>>data Dec =
>> ClassD Cxt Name [Name] [FunDep] [Dec]
>> InstanceD Cxt Type [Dec]
>>Only one 'Type' can be given for an instance.
> And there _should_ only be one type. Checkout 'appT'.
> Some real documentation for TH would clear misconceptions such as this.
Is that really how this is done? That doesn't seem like it can be right:
instance X (a b) -- single parameter class where 'a' has an arrow kind
is very different from:
instance X a b -- multiple parameter class
I would expect a type constructed with 'appT' to correspond to the first
declaration, and not to the second.
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