When parsing input with scanf, for example with the pattern "%d %d\n", I often need to write fun x y -> x, y.
Is there a function in the standard library to replace this expression? pair, tuple, (,), don't seem to be defined.
To the best of my knowledge this does not exist as part of Stdlib.
Having a make2tuple function seems straightforward: let make2tuple a b = (a, b), but so does make3tuple and make4tuple, etc, etc. When is enough enough? Where do you draw the line?
This doesn't seem particular better than writing fun a b -> (a, b) or fun a b c -> (a, b, c) as needed. If they're needed often, you can create utility functions for this in your code.
Just be aware of the value restriction if you try to use partial function application with this:
# let mk2tuple a b = (a, b);;
val mk2tuple : 'a -> 'b -> 'a * 'b = <fun>
# let make_tuple_with_5 = mk2tuple 5;;
val make_tuple_with_5 : '_weak1 -> int * '_weak1 = <fun>
# make_tuple_with_5 2;;
- : int * int = (5, 2)
# make_tuple_with_5;;
- : int -> int * int = <fun>
# make_tuple_with_5 7.3;;
Error: This expression has type float but an expression was expected of type
int
# mk2tuple 5 7.3;;
- : int * float = (5, 7.3)