Hi.
Your function gets passed numbers one by one in the place of x, and its
previous result in the place of acc, and it returns a Bool. Initial value
in place of acc parameter ("previous result") is put as False (since you
begin with answer "no" to question "is it elem?").
Hope this helps.
24 вер. 2015 19:04 "goforgit ."
Reading http://learnyouahaskell.com/higher-order-functions
I understand that with the function
sum' :: (Num a) => [a] -> a sum' = foldl (+) 0
the call
ghci>>> sum' [1,2,3]
will be evaluated as
0 + 1 + 2 + 3 = 6
But what about the function
elem' :: (Eq a) => a -> [a] -> Bool elem' y ys = foldl (\acc x -> if x == y then True else acc) False ys
and calling it with
ghci>>> elem' 3 [1,2,3]
How is that evaluated to True by foldl in elem'?
Thanks in advance for any explanation to this!
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