Question

For example, instead of

- op =;
val it = fn : ''a * ''a -> bool

I would rather have

- op =;
val it = fn : ''a -> ''a -> bool

for use in

val x = getX()
val l = getList()
val l' = if List.exists ((op =) x) l then l else x::l

Obviously I can do this on my own, for example,

val l' = if List.exists (fn y => x = y) l then l else x::l

but I want to make sure I’m not missing a more elegant way.

Answer 1

You could write a helper function that curries a function:

fun curry f x y = f (x, y)

Then you can do something like

val curried_equals = curry (op =)
val l' = if List.exists (curried_equals x) l then l else x::l