[Haskell-cafe] let vs. where
cmb21 at kent.ac.uk
Wed Nov 14 04:16:55 EST 2007
> A let clause would work fine here:
> someFunction ls a b c = let listLen = length ls
> someAuxFunction x y = ... listLen ...
> someOtherFunction x y = ... listLen ...
> ... listLen ...
> it's just that you don't want to mix let and where clauses, because then
> things get confusing. Even if it worked with both, noone would know the
> binding rules.
Possibly in that case, but there are cases where I believe they are not
gg n = ([1..,10^6*n], [1..10^6*n])
exp = (fst $ gg 1000, snd $ gg 1000)
this could be captured nicely in a where clause:
exp = (fst blah, snd blah) where blah = gg 1000
But a let would have to be placed in both elements of the tuple - and
therefore being evaluated twice (unless the implementation is smart enough
to work out they can be shared?):
exp = (let blah = g 1000 in fst blah, let blah = g 1000 in snd blah)
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