Re: [Haskell-cafe] Type Classes in Haskell - how can I make GHC make a choice of types, when the type chosen doesn't matter?

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 wrote:

On 14 April 2011 20:35, Chris Dew 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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