Hi Albert,
Thanks for your response (and sorry about my earlier email missing some
content at the end; I rushed out to lunch as I was sending this).
Your solution works fine. It's better than the option I've listed.
On Wed, Dec 23, 2015 at 7:57 AM, Albert Y. C. Lai
On 2015-12-20 08:01 PM, Noon Silk wrote:
{-# LANGUAGE NoMonomorphismRestriction #-}
data Status = Foo | Bar
data Rec m a = Rec { get :: m a , status :: Status }
defRec :: (Monad m) => Rec m a defRec = undefined
myRec :: (Monad m) => Rec m a myRec = Rec x y where Rec x y = defRec
Why this is an ambiguous-type error is a really long story. But a factor is analogous to "show . read". Another factor is that since you turn off the monomorphism restriction, there is a type generalization step, and the generalizing of y's type is separate from the generalization of x's type.
I have found this solution, it works by connecting types to suppress the generalize step:
{-# LANGUAGE NoMonomorphismRestriction, ScopedTypeVariables #-} ... myRec :: forall m a. (Monad m) => Rec m a myRec = Rec x y where Rec x y = defRec :: Rec m a
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-- Noon Silk, ن https://sites.google.com/site/noonsilk/ "Every morning when I wake up, I experience an exquisite joy — the joy of being this signature."