Hi Daniel, I took the code that accompanies the paper and I'm trying to use it but I can't figure out how to get started. I have the following code but it is not giving me the expected result: import TypingHaskellInHaskell mapt = "map" :>: Forall [Star, Star] ([] :=> ((TGen 0 `fn` TGen 1) `fn` TAp tList (TGen 0) `fn` TAp tList (TGen 1))) idt = "id" :>: Forall [Star] ([] :=> (TGen 0 `fn` TGen 0)) exprt = Ap (Const mapt) (Const idt) test = runTI $ tiExpr initialEnv [] exprt When I execute the test function above in ghci I get: ([],TVar (Tyvar "v3" Star)). I was expecting someting like below for the type part: TAp tList (TGen 0) `fn` TAp tList (TGen 0) What I want is the library to compute for me the type of "map id". What is the proper way to achieve this? Thanks a lot, Patrick On Wed, Jul 6, 2011 at 8:19 AM, Patrick LeBoutillier wrote:

Daniel,

The paper you recommend seems like very interesting stuff.  I will definitely look at it closer.

Thanks a lot,

Patrick

On Tue, Jul 5, 2011 at 3:24 PM, Daniel Fischer wrote:

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On Tuesday 05 July 2011, 19:55:43, Patrick LeBoutillier wrote:

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Hi all,

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Here's my question: Does ghci have a verbose mode or something where is can show you step by step how the types are worked out?

No. You can use it to get the types of subexpressions, though, and work towards the complete expression from that:

Prelude> :t (:) (:) :: a -> [a] -> [a] Prelude> :t (. (:)) (. (:)) :: (([a] -> [a]) -> c) -> a -> c Prelude> :t (map . (:)) (map . (:)) :: a -> [[a]] -> [[a]]

which gives you smaller gaps to fill in.

...

If not is there a hackage (or any other kind of) package that can do that?

I'm not aware of any, but there might be.

...

a lot, so I was wondering if such a program existed that could do it automatically.

Automatic type checkers do exist (every compiler/interpreter needs one), but I don't think they have been written with the ability to output not only the result but also the derivation.

For someone familiar with a particular type checker, it probably wouldn't be hard to add that feature, but if it's a complicated beast like GHC's type checker, becoming familiar with it would probably be a big undertaking.

Writing your own much-reduced (able to parse and typecheck only a very restricted subset of the language) might be easier, but probably working from Mark P. Jones' "Typing Haskell in Haskell" http://web.cecs.pdx.edu/~mpj/thih/ would be better than starting from scratch (it's somewhat oldish, so it certainly doesn't cope with recent GHC extensions, but for everyday run-of- the-mill problems, it should be working with only minor modifications).

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada