[Haskell-cafe] CPS versus Pattern Matching performance

[Tony Morris]

Thanks for the explanations - fully understood.

Tony Morris
http://tmorris.net/



Jonathan Cast wrote:
> On Tuesday 10 July 2007, Tony Morris wrote:
>> Thanks Don,
>> Is your explanation specific to maybe? Or does that apply to all functions?
>>
>> Suppose the following function for lists:
>>
>> f :: [a] -> b -> (a -> [a] -> b) -> b
>>
>> ...instead of pattern matching [] and (x:xs)
> 
> Of course.  GHC doesn't know anything about maybe; all it sees is:
> 
> 1. One-liner:
> 
> maybe f x mb = case mb of { Just x' -> f x'; Nothing -> x }
> 
> 2. Non-recursive
> 
> And it inlines like crazy.  If you had quite a large data type, the number of 
> case alternatives /might/ put you over GHC's inlining threshold, but that 
> (ridiculous) scenario is the only thing that'll keep the argument from 
> generalizing to your use case.
> 
> <snip>
> 
> Jonathan Cast
> http://sourceforge.net/projects/fid-core
> http://sourceforge.net/projects/fid-emacs
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