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Comment by spion | Hacker News Reader

It returns the multiply-by-2 function. This turns out to be super useful

  map (* 2) [1, 2, 3]

will take that function and apply it to each element in the list [1,2,3].

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That map function looks a lot like it has 2 arguments, a function and an operand array (ie a list)??

map takes a function and returns a function that takes a list and returns a list. It has a type like: (a->b) -> [a] -> [b] (I take a function from type a to type b and return a function from list of a to list of b)

define

double_list_elements = map (*2)

and

> double_list_elements [1, 2, 3, 4]

gives you [2, 4, 6, 8]

Again, it works the same way. The map function takes the argument (*2) and returns a function, which is then applied to the list.

Seems like a semantic gloss, but then at some level I suppose higher level computing languages are all a semantic gloss.

Thanks for the responses - I'm now almost as knowledgeable as a 10 yo prior to being instructed in the subject at hand.

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