Unit testing for uncurry in ocaml

Question

my implementation so far I cant seem to understand where is the issue

let uncurry_test1 _test_ctxt =
    assert_equal
    uncurry  f  (4 3)
    7
    

Answer 1

The assert_equal function from the OUnit2 library has type,

val assert_equal :
  ?ctxt:test_ctxt ->
  ?cmp:('a -> 'a -> bool) ->
  ?printer:('a -> string) ->
  ?pp_diff:(Format.formatter -> ('a * 'a) -> unit) ->
  ?msg:string -> 'a -> 'a -> unit

There are only two non-keyword parameters, but you're applying it to four. I would suggest you read at least the OCaml tutorial and learn how functions are applied in OCaml. For example, the piece of code (4 3) in OCaml means apply 4 to 3, where "apply F to Y" means call the function F with argument X. Obviously, 4 is not a function (spoiler, it is a number), so this code doesn't make sense and raises a type error.

It is hard to guess from the information that you provided what is the type of uncurry and what is the type of f, but probably you meant something like this,

assert_equal 7 (uncurry f 4 3)

Which says, that we expect 7 when we uncurry the function f and apply it to 4 and 3.

where f is probably curry (+)