How can this function be simplified?

Question

This is the function:

f []      = []
f (h:t)   = (\x -> x - h) : f t

It takes a list and returns a list of anonymous functions, that substract each each element from x.

Apparently there is some way to write this whole function in 20 characters or less.

I tried to do it with map but that just applies a function to each element of the list. I also tried to replace the anonymous function with (-a) which didn't work either.

Does anybody have an idea?

Seems like a perfect question for https://codegolf.stackexchange.com/ — jwd, Jul 10 '17 at 18:50
Shouldn't the correct function be: `f (h:t) = (\x -> x - h) : f t`. — Willem Van Onsem, Jul 10 '17 at 18:51
@Carcigenicate That's a bit of a strange corner of the Haskell syntax. `(- h)` means to negate the number `h`. `subtract h` would be equivalent to that lambda. — David Young, Jul 10 '17 at 18:51
@Carcigenicate Unfortunately, no: `(-h)` is unary minus, and not a section! That's why we have `subtract h` from the `Prelude`. — chi, Jul 10 '17 at 18:52

Willem Van Onsem · Answer 1 · 2017-07-10T21:16:39.943

7

You can simply use:

f :: Num a => [a] -> [a -> a]
f = map subtract

Since subtract :: Num n => n -> n -> n, it thus means that we map every element h from the list to a function subtract h. Subtract h subtracts h from any given value x. So subtract h x == x - h.

edited Jul 10 '17 at 21:16

answered Jul 10 '17 at 18:52

Willem Van Onsem

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How can this function be simplified?

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