OCaml constructor unpacking
ocaml, syntax
Solution
This is a tricky part of OCaml syntax. If you define your type as you show, its constructor `Foo` expects two values in parentheses. And it always has to be two values, it's not a single value that's a tuple.
If you're willing to use a different type, you can do something more like what you want:
# type bar = Bar of (int * string);;
type bar = Bar of (int * string)
# let Bar data = Bar (3, "foo");;
val data : int * string = (3, "foo")
# let Bar (d1, d2) = Bar (3, "foo");;
val d1 : int = 3
val d2 : string = "foo"
When declared this way, the constructor `Bar` expects one value that's a tuple. This can be more flexible, but it also takes a little more memory to represent it, and a little longer to access the parts.
Problem
Is it possible to unpack a type by binding its data to a single value instead of a tuple? ``` # type foo = Foo of int * string;; type foo = Foo of int * string # Foo (3; "bar");; Foo (3; "bar");; Error: The constructor Foo expects 2 argument(s), but is applied here to 1 argument(s) # Foo (3, "bar");; - : foo = Foo (3, "bar") # (* Can this possibly work? *) # let Foo data = Foo (3, "bar");; let Foo data = Foo (3, "bar");; Error: The constructor Foo expects 2 argument(s), but is applied here to 1 argument(s) # (* Here is the version that I know works: *) # let Foo (d1, d2) = Foo (3, "bar");; val d1 : int = 3 val d2 : string = "bar" ``` Is this syntactically possible?