CODEWITHSUNDEEP
ocamlprimes
송재민
송재민

Reputation: 63

Trouble in Making an isPrime Function

This is a homework. OCaml seems to be made by a psychopath.

    let prime : int -> bool
= fun n ->
    if n > 2 then 
        let a = n - 1 in
        let rec divisor n a =
            if a > 1 && n mod a = 0 then false
        else if a = 2 && n mod a <> 0 then true
        else divisor n a-1 ;;
    else if n = 2 then true
    else if n = 1 then false

I am not good at coding and I know that my isPrime algorithm is wrong. But I wonder where in my code is the mistake that produces the syntax error.

Also is there any way to define the isPrime function in a recursive form?

Example:

let rec prime n = ~

Upvotes: 2

Views: 1452

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66813

You'll get better responses from experts if you don't gratuitously insult their language :-) But I'm an easygoing guy, so I'll take a stab at your syntax error.

There are quite a few problems in this code. Here are 3 that I see right off:

  1. The symbol ;; is used to tell the interpreter that you've entered a full expression that you want it to evaluate. It's definitely out of place in the middle of a function declaration.

  2. Your second let doesn't have an associated in. Every let must have an in after it. The only exception is for defining values at the top level of a module (like your prime function).

  3. The expression divisor n a-1 is parsed as (divisor n a) - 1. You want parentheses like this: divisor a (n - 1).

Upvotes: 4

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