CODEWITHSUNDEEP
integerocaml
OrenIshShalom
OrenIshShalom

Reputation: 7172

ocaml int and unsigned int

I am trying to find the last occurrence of some integer in an array in ocaml:

let rec findLastHelper l i loc ret =
  match l with
  | [] -> ret
  | x::xs ->
        match x == i with
        | true -> findLastHelper xs i (loc+1) loc
        | _ -> findLastHelper xs i (loc+1) ret ;;

let findLast l i = (findLastHelper l i 0 -1) ;;
(* let findLast l i = (findLastHelper l i 0 493) ;; *)

let main = Printf.printf "%d\n" (findLast [ 1 ; 6 ; 8 ; 2 ; 9 ; 8 ] 7) ;;

If the integer doesn't exist, the code should return -1. When I compiled it, I got the following error:

$ ocamlopt main.ml -o main
File "main.ml", line 9, characters 20-40:
Error: This expression has type int -> int
       but an expression was expected of type int

When I replace the -1 with some arbitrary positive value (493 above), everything goes fine. What is going on here?

Upvotes: 3

Views: 400

Answers (1)

corwin.amber
corwin.amber

Reputation: 423

OCaml is interpreting - as a binary operator in this context. You have to parenthesize (-1).

This is a common OCaml gotcha.

Upvotes: 3

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