[Haskell] Re: Rebindable syntax for monads and arrows

Ashley Yakeley ashley at semantic.org
Tue Jan 11 01:01:56 EST 2005

Simon Peyton-Jones <simonpj at microsoft.com> wrote:

> But I suspect that programmers will prefer a more woolly rule that does
> as much constraint solving as it can (provided all instance selection is
> uniquely determined).  That would give the slightly surprising behaviour
> I describe above if an overlapping instance declaration was added.

Is this only an issue when

1. overlapping instances are allowed, and
2. a type-signature is omitted?

I agree surprising behaviour is bad. If the ambiguity can always be 
resolved by giving a type-signature, perhaps GHC should simply give a 
warning in these cases?

My own attitude tends towards "if you don't specify type signatures, you 
get what you deserve", especially as I freely use implicit parameters.

Ashley Yakeley, Seattle WA

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