Function Composition
In Haskell, the
.
operator represents represents
function composition
. That is to say,
(f.g) x = f(g(x))
Using the type variables
a
,
b
and
c
, what would be the type of the function composition operator itself?
-
(a -> b) -> (c -> a) -> c -> b -
a -> b -> c -> a -> c -> b -
(a -> b) -> (c -> a) -> b -> c -
(a -> b) -> (c -> a) -> a -> c -
(a -> b) -> (b -> c) -> a -> c
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1 solution
Note that for function composition to be able to compose f ∘ g , the range of g must be in the domain of f .
That is why the answer is
( a -> b) -> (c -> a) -> c -> b