OCaml meaning of "in"-CodePudding

Lets assume the following function

val foo : int -> int -> bool -> int

let foo x y b = 
  let x,y = if x > y then y,x else x,y in
  let rec loop x y b =
    if x >= then x
    else if b then loop (x 1) y (not b)
    else loop x (y-1) (not b)
  in
  loop x y b

I still don't quite understand the concept of the "in". Does the line mean "let x,y = ... in" that it is executed immediately or only when you "Call" it? And when i dont need to call it why do i need the last line loop x y b? Thanks in advance :)

CodePudding user response：

in is just part of the OCaml syntax - let PATTERN = EXPR1 in EXPR2 is an expression which binds the result of EXPR1 to PATTERN and then evaluates EXPR2 with the new bindings present. In some languages like F# and Haskell, you don't (always) need in - it's inferred from the indentation. OCaml syntax is indentation insensitive which requires it to have an explicit in.

Does the line mean "let x,y = ... in" that it is executed immediately or only when you "Call" it?

It's evaluated immediately.

And when i dont need to call it why do i need the last line loop x y b?

In this code, the previous line defines a function named loop with 3 arguments, and then later you call the function with the arguments x y b.