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     operator or (operand1, operand2: Boolean) = Result: Boolean;


     operator or (operand1, operand2: integer_type) = Result: integer_type;


     procedure or (var operand1: integer_type; operand2: integer_type);


In GNU Pascal, or has three built-in meanings:

  1. Logical “or” between two Boolean-type expressions. The result of the operation is of Boolean type.

    By default, or acts as a short-circuit operator in GPC: If the first operand is True, the second operand is not evaluated because the result is already known to be True. You can change this to complete evaluation using the --no-short-circuit command-line option or the {$B+} compiler directive.

  2. Bitwise “or” between two integer-type expressions. The result is of the common integer type of both expressions.
  3. Use as a “procedure”: operand1 is “or”ed bitwise with operand2; the result is stored in operand1.

Conforming to

The logical or operator is defined in ISO 7185 Pascal.

According to ISO, you cannot rely on or being a short-circuit operator. On the other hand, GPC's default behaviour does not contradict the ISO standard. (See or_else.) However, since it seems to be a de-facto standard among ISO Pascal compilers to evaluate both operands of or, GPC switches to --no-short-circuit mode if one of the language dialect options selecting ISO Pascal, for instance --extended-pascal, is given. Use --short-circuit to override.

Use of or as a bitwise operator for integers is a Borland Pascal extension.

Use of or as a “procedure” is a GNU Pascal extension.


     program OrDemo;
       a, b, c: Integer;
       if (a = 0) or (b = 0) then  { logical `or' }
         c := 1
       else if (a or b) = 0 then  { bitwise `or' }
         c := 2
         or (c, a)  { same as `c := c or a' }

Note the difference between the logical or and the bitwise or: When a is 2 and b is 4, then a or b is 6. Beware: a or b = 0 happens to mean the same as (a = 0) and (b = 0). (Note the and!)

Since bitwise or has a higher priority than the = operator, parentheses are needed in if (a = 0) or (b = 0) because otherwise 0 or b would be calculated first, and the remainder would cause a parse error.

See also

Keywords, and, xor, Operators.