[Haskell-beginners] will GHC optimize pattern-matching on integers?

[Rahul Muttineni]

Hi Patrick,

Yes, this will optimise to "a nice balanced tree of decisions with dense
jump tables in the leafs" [1]. You can check out the comments in [1] for
more details.

[1] https://github.com/ghc/ghc/blob/master/compiler/cmm/CmmSwitch.hs#L37

Hope that helps,
Rahul

On Thu, Apr 13, 2017 at 3:55 AM, Patrick Pelletier <code at funwithsoftware.org
> wrote:

> Suppose I am doing a pattern match on a large number of consecutive (or
> mostly-consecutive) integers:
>
> foo 0 = something
> foo 1 = somethingElse
> ...
> foo 1000 = anotherThing
>
> Will GHC optimize this to a table lookup, or is it going to test each
> integer in turn?  Am I better off using a Vector or Map instead of pattern
> matching?
>
> Thanks,
>
> --Patrick
>
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-- 
Rahul Muttineni
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