[Haskell-beginners] Trying to understand the foldl type?

Bob Ippolito bob at redivi.com
Tue Dec 24 13:47:23 UTC 2013


Given foldl (+) 0 [1..10]
(+) is (a -> b -> a)
0 is a
[1..10] is [b]
and the final a is the result of the expression.

On Tuesday, December 24, 2013, Angus Comber wrote:

> The type is:
>
> foldl :: (a -> b -> a) -> a -> [b] -> a
>
> Eg I might do something like this:
>
> foldl (+) 0 [1..10]
>
> so taking (a -> b -> a)
>
> leftmost a is (+)
> b is 0
> right a is what?  The first value in the list?
>
> Then -> ?
>
> [b] ?  Is this like the temporary recursion calculation?
>
> final -> a is the result?
>
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