Node:User-defined Operators, Previous:Built-in Operators, Up:Operators

#### User-defined Operators

GNU Pascal allows the (re-)definition of binary operators according to the Pascal-SC (PXSC) syntax. The following vector addition example illustrates how to do this:

    program OperatorDemo;

    type
      Vector3 = record
        x, y, z: Real;
      end;

    var
      a, b, c: Vector3 = (1, 2, 3);

    operator + (u, v: Vector3) w: Vector3;
    begin
      w.x := u.x + v.x;
      w.y := u.y + v.y;
      w.z := u.z + v.z;
    end;

    begin
      c := a + b
    end.

Between the closing parenthesis of the argument list and the result variable (`w` in the above example), GPC allows an optional equal sign. This is not allowed in PXSC, but it is consistent with Extended Pascal's function result variable definitions, where the equal sign is obligatory (but also optional in GPC).

The argument types needn't be equal, and the name of the operator may be an identifier instead of a known symbol. You cannot define new symbols in GPC.

The PXSC operators `+>`, `+<`, etc. for exact numerical calculations currently are not implemented in GPC, but you can define them. Also, the other real-type operators do not meet the requirements of PXSC; a module which fixes that would be a welcome contribution.