On Tue, Jan 26, 2010 at 11:24 PM, Eduard Sergeev
Xingzhi Pan wrote:
The first argument to foldr is of type (a -> b -> a), which takes 2 arguments. But 'step' here is defined as a function taking 3 arguments. What am I missing here?
You can think of step as a function of two arguments which returns a function with one argument (although in reality, as any curried function, 'step' is _one_ argument function anyway): step :: b -> (a -> c) -> (b -> c)
e.g. 'step' could have been defined as such: step x g = \a -> g (f a x)
to save on lambda 'a' was moved to argument list.
Right. But then step is of the type "b -> (a -> c) -> (b -> c)". But as the first argument to foldr, does it agree with (a -> b -> a), which was what I saw when I type ":t foldr" in ghci?
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