Re: [Haskell-cafe] I love purity, but it's killing me.

tomahawkins:

On 2/8/08, Emil Axelsson wrote:

...

I know of a few of ways to express sharing in a pure language:

1) "Observable sharing", which, in general, is unsafe. 2) Using Template Haskell 3) Matthew Naylor has done some work on "expressible sharing", which has 4) Use a monad (but I'm sure this is what you're trying to avoid).

Or...

5) Forget embedding the DSL, and write a direct compiler.

In addition to the sharing problem, another shortcoming of Haskell DSLs is they can not fully exploit the benefits of algebraic datatypes. Specifically, pattern matching ADTs can only be used to control the compile-time configuration of the target, it can't be used to describe the target's behavior -- at least for DSLs that generate code that executes outside of Haskell's runtime.

Writing a real compiler would solve both of these problems. Is there any Haskell implementation that has a clean cut-point, from which I can start from a fully type-checked, type-annotated intermediate representation?

Taking the output of GHC's intermediate phase, after optimising leaves you with type checked, optimised, 'Core' -- basically lambda calculus with extras. It's a good start if you then want to hand-compile that down. Extract it with -fext-core -- Don