Re: [Haskell-cafe] Proof that Haskell is RT

Lennart Augustsson wrote:

You can't write a straightforward dynamic semantics (in, say, denotational style) for Haskell. The problem is that with type classes you need to know the types compute the values. You could use a two step approach: first make a static semantics that does type inference/checking and translates Haskell into a different form that has resolved all overloading. And, secondly, you can write a dynamic semantics for that language.

But since the semantics has to have the type inference engine inside it, it's going to be a pain.

It's possible that there's some more direct approach that represents types as some kind of runtime values, but nobody (to my knowledge) has done that.

This has been done. For example, check out the type class semantics given in Thatte, Semantics of type classes revisited, LFP '94 Stuckey and Sulzmann, A Theory of Overloading, TOPLAS'05 Harrison: A Simple Semantics for Polymorphic Recursion. APLAS 2005 is also related I think. The ICFP'08 poster Unified Type Checking for Type Classes and Type Families , Tom Schrijvers and Martin Sulzmann suggests that a type-passing semantics can even be programmed by (mis)using type families. - Martin

-- Lennart

On Wed, Nov 12, 2008 at 12:39 PM, Luke Palmer wrote:

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On Wed, Nov 12, 2008 at 3:21 AM, Jules Bean wrote:

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Andrew Birkett wrote:

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Hi,

Is a formal proof that the Haskell language is referentially transparent? Many people state "haskell is RT" without backing up that claim. I know that, in practice, I can't write any counter-examples but that's a bit handy-wavy. Is there a formal proof that, for all possible haskell programs, we can replace coreferent expressions without changing the meaning of a program?

The (well, a natural approach to a) formal proof would be to give a formal semantics for haskell.

Haskell 98 does not seem that big to me (it's not teeny, but it's nothing like C++), yet we are continually embarrassed about not having any formal semantics. What are the challenges preventing its creation?

Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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