[Haskell-beginners] Working out the types

[Patrick LeBoutillier]

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
<daniel.is.fischer at googlemail.com> wrote:
> On Tuesday 05 July 2011, 19:55:43, Patrick LeBoutillier wrote:
>> Hi all,
>
>> 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