[Haskell-cafe] Re: type families and type signatures
Tom.Schrijvers at cs.kuleuven.be
Wed Apr 9 05:04:57 EDT 2008
> However, I have this feeling that
> bar :: forall a . Id a -> String
> with a type family Id *is* parametric in the sense that no matter what a
> is, the result always has to be the same. Intuitively, that's because we may
> not "pattern match on the branch" of a definition like
> type instance Id String = ..
> type instance Id Int = ..
But in a degenerate case there could be just this one instance:
type instance Id x = GADT x
which then reduces this example to the GADT case of which you said that is
was "clearly parametric".
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e-mail: tom.schrijvers at cs.kuleuven.be
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