[Haskell-cafe] Why is Haskell so slow (comparing to Java/Scala)?

[Saurabh Nanda]

Intresting. Wont using "void" or "_ <- forM blah" have the same effect? Why
not?

On 20-Sep-2017 9:37 PM, "Nick Smallbone" <nick at smallbone.se> wrote:


Hi Stanislav,

Станислав Черничкин <schernichkin at gmail.com> writes:
> I've wrote simple Haskell benchmark program, which populated primitive
vector
> from vector package:
>
> ...
> void $ for [0..1000000 - 1] $ flip (P.unsafeWrite v) (1 :: Int)

'for' is a variant of 'map' - it returns a list of results (in this case
a list of a million () values). Instead you should use 'forM_' (note the
underscore) from Control.Monad, which discards the result - that cuts
the runtime by a huge amount when I try it. (And make sure to compile
with -O too.)

Nick

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