[Haskell-cafe] Re: Is my code too complicated?

Ben Millwood haskell at benmachine.co.uk
Mon Jul 5 20:51:45 EDT 2010

On Mon, Jul 5, 2010 at 2:41 PM, Ertugrul Soeylemez <es at ertes.de> wrote:
> Yes, there is some performance loss because of wrapping/unwrapping, but
> I think this loss is neglible for most applications.  And I'd ask
> anyway.  This is a discussion thread after all. =)

Pretty much all monad transformers are implemented as newtypes, so the
wrapping and unwrapping operations themselves should get compiled into
nothing, I think. It may be that the extra type faff makes inlining or
other arcane optimisations less straightforward, but I see no reason
to assume that monad transformers are necessarily even slightly slower
than explicitly-constructed amalgamations.

In my experience, something like ReaderT Params (StateT SessionData
IO) a may *look* scary, but in all your code you just use ask and put
and get anyway and they all work like magic - the difficult bits are
generally speaking hidden in your type synonyms and run function.

But then, my largest haskell projects have never been more than a
thousand or so lines, so perhaps it's just an issue of scale.

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