[arjunnarayan]

There are two things to remember. The first is the match binding thing that tomp mentions in his reply.

The second one is that in OCaml, semicolon is a separator, and not a terminator. In contrast, in C/C++, semicolon is a terminator. If you have an expression, you end it with a ";" just because.

This is not the case for OCaml. In OCaml, semicolon is used to separate two sequential expressions where only one expression is expected. Thus,

    <expr1>;<expr2> 

is evaluated in sequence, and can be used in a place where only one is expected. For example, if statements have the following syntax:

    if <expr1> then <expr2> else <expr3>

Now if you wanted to do two things (instead of one) in the "then" block, you would simply write

    if <expr1> then <expr2.1>;<expr2.2> else <expr3>

Notice that under these rules

    if <expr1> then <expr2>; else <expr3> 

makes no sense. Separators are not terminators. We are used to thinking of ";" as terminators because of C/C++.

[p4bl0]

    if <expr1> then <expr2.1>;<expr2.2> else <expr3>

Actually, this will not work, I was also confused by it.

    # if true then (); 1 else 2;;
    Error: Parse error: [str_item] or ";;" expected (in [top_phrase])
    # if true then begin (); 1 end else 2;;
    - : int = 1
    # if true then ((); 1) else 2;;
    - : int = 1

The confusion comes from the fact that it doesn't behave the same way in match expressions:

    # match true with | true -> (); 1 | false -> 2;;
    - : int = 1

[mercurial]

I'll add that you need ';'-as-separator (you also use ';' in other places, such as when separating items in a list) only when calling functions which return 'unit', which is typically functions which perform side-effects (eg, close a file). That's usually a small portion of your program.