Question

You could pattern-match against multiple arguments of a function by creating a tuple and then destructuring it in a match expression:

let f x y =
  match x, y with
  | pattern1 -> expr1
  | ...

Alternatively, if you don’t need a curried function, you could do this by making f take a tuple as the only argument:

let f (x, y) = function
  | pattern1 -> expr1
  | ...

The advantage of the latter method is that you don’t have to write the arguments twice every time you define a function. But functions that take a tuple seems to be not as popular than curried ones.

So which of the two is deemed canonical, or preferred, in the OCaml community?

EDIT: Just as pad pointed out below, I mean let f = function blah blah in the second code snippet.

Answer 1

A tuple is not just a syntactic construct, it represents a real data structure. This means that fun (x,y) is (very slightly) less efficient than f x y in the case were x and y aren’t already tupled, because a tuple has to be allocated. If this isn’t clear, the rough equivalent in Java would be

void foo(X x, Y y) { ... }
void bar(Tuple<X,Y> t) { ... }

/* client code */
X x = new X();
Y y = new Y();

foo(x, y);  // Just uses x and y directly
bar(new Tuple<X,Y>(x, y)); // Has to "new" a Tuple

For this reason, it’s generally preferable to avoid using tuples as function arguments unless you have a good reason to do so.

P.S. A similar consideration applies to datatype declarations, where the following are subtly different:

type 'a foo = Foo of 'a * 'a;
type 'a bar = Bar of ('a * 'a);

Foo is a datatype constructor that takes two arguments. Bar is a constructor that takes one argument (a tuple).