Where did you get that definition?

"function that takes one argument and returns one value of the same type" is the identity function.

Identity function returns the same _value_.

If it's only the same _type_, but the value is not the same, then it's an endomorphism. The function definitions look the same `a -> a`.

string reversal, integer negation or toUpperCase are classical examples of endomorphisms.

Identity is a specific case of endomorphism.

string reversal, integer negation or toUpperCase are classical examples of functions which will not compile as `a -> a`

The function which will compile as `a -> a` is the identity function.

	▲	epolanski 2 days ago \| parent [-]
		That's correct, but I'm not sure how it relates to my comment as I said that `a -> a` is just an endomorphism. identity, uppercase or negate are all endomorphisms, with identity being the only generic one.