Usefulness (as in practical applications) of Currying v.s. Partial Application in Scala

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Currying is mostly used if the second parameter section is a function or a by name parameter. This has two advantages. First, the function argument can then look like a code block enclosed in braces. E.g.

using(new File(name)) { f =>
  ...
}

This reads better than the uncurried alternative:

using(new File(name), f => {
  ...
})

Second, and more importantly, type inference can usually figure out the function’s parameter type, so it does not have to be given at the call site.
For instance, if I define a max function over lists like this:

def max[T](xs: List[T])(compare: (T, T) => Boolean)

I can call it like this:

max(List(1, -3, 43, 0)) ((x, y) => x < y)

or even shorter:

max(List(1, -3, 43, 0)) (_ < _)

If I defined max as an uncurried function, this would not work, I’d have to call it like this:

max(List(1, -3, 43, 0), (x: Int, y: Int) => x < y)

If the last parameter is not a function or by-name parameter, I would not advise currying. Scala’s _ notatation is amost as lightweight, more flexible, and IMO clearer.

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