Re: [Haskell-cafe] Maybe won't let me count

Mmm strange... I thought I read somewhere that succ is faster, but now I'm searching for the reference and don't find it. Anyway, good to know! Best, Antonio Regidor Garcia El Mon, Mar 29, 2021 at 04:22:07AM -0400, Viktor Dukhovni escribió:

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On Mar 29, 2021, at 3:36 AM, Antonio Regidor Garcia wrote:

succ n is n+1 but faster than the function (+).

Because 'succ' typically does bounds checks, while (+) (for Int) just does the underlying CPU instruction, that's not particularly plausible.

Indeed running a test (100 million increments) suggests that (+) is noticeably cheaper:

(1 +): MUT time 0.035s ( 0.035s elapsed) (succ): MUT time 0.134s ( 0.134s elapsed)

The succ function is however safer against uncaught overflow:

λ> succ False True λ> succ True *** Exception: Prelude.Enum.Bool.succ: bad argument

If the datatype in question is not bounded (Double, Integer, ...) then succ performance is closer to that of (+). I see identical speeds for Double, but (GHC 8.10 on X86_64) succ seems slightly slower for Integer.

-- Viktor.

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