Thanks, that link's very relevant to what I'm trying. For the time
being I'll accept a partial solution where the last two types are now
the same, and try to improve it when my knowledge of Haskell improves.
I really want ("hello" ->> bracket) in ("hello" ->> bracket ->>
putStrLn) to have a type of "String". Using the partial solution
which Neil Brown proposed, the code will work, but ("hello" ->>
bracket) will have a type of "IO String" which *seems* like it will be
less efficient.
All the best,
Chris.
On 14 April 2011 21:22, Stephen Tetley <[email protected]> wrote:
> On 14 April 2011 20:35, Chris Dew <[email protected]> wrote:
>
>> Could you suggest how these constraints could be expressed in the
>> Haskell type system?
>>
>
> Hi Chris
>
> I'm afriad I'd have to decline - generally in Haskell implicit
> "lifters" are problematic, so it isn't something I'd be looking to
> solve.
>
>
> There was a thread on Haskell Cafe about them last November called
> "Making monadic code more concise", that you might find interesting -
> especially Oleg Kiselyov's comments:
>
> http://www.haskell.org/pipermail/haskell-cafe/2010-November/086445.html
>
> Best wishes
>
> Stephen
>
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