Is there a way to get the curried form of binary operators in SML / NJ?

Question

For example, instead of

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

I would prefer

- 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 it myself, for example,

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

but I want to make sure that I don’t miss a more elegant way.

Answer 1

You can write a helper function that performs the 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

Answer 2

My knowledge of SML is scarce, but I looked through the Ullman book and couldn't find an easy way to convert a function that takes a tuple to a curried function. They have two different signatures and cannot be directly compatible with each other.

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