CODEWITHSUNDEEP
ocaml
P.C.
P.C.

Reputation: 649

How can forcibly get an OCaml function to return an int type value instead of unit?

I am new to OCaml.

I am working on some code in which the following function is nested inside another function, which must return an int type value.

Asn(x,e) ->
      let v = eval e in
        Array.set vararr x+1 v

vararr is a global array already declared and initialised above.

In this function, I want to set an element of the array using "Array.set vararr x+1 v", but I want the function to return the value v. How can I do that?

Update:

I changed it to:

Asn(x,e) ->
      let v = eval e in
        Array.set vararr x+1 v; 
      v

The error for "Array.set vararr x+1 v;" is:

This expression has type int -> unit
       but an expression was expected of type int

I think the problem isn't what Asn returns. The problem is with what "Array.set vararr x+1 v;" returns. This is very strange! Why does "Array.set vararr x+1 v;" have to return an int type value?

Upvotes: 0

Views: 970

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66793

I think you want this:

let v = eval e in
Array.set vararr (x + 1) v;
v

Update

Don't forget parentheses around (x + 1).

The expression:

Array.set vararr x+1 v

Is parsed like this:

(Array.set vararr x) + (1 v)

Function application in OCaml has very high precedence.

The + operator wants an int at the left but you have a function there.

Generally speaking, you just need to get used to OCaml syntax. It's not so bad after a little experience.

Upvotes: 4

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