M2compiler-V3/compiler/tests/t_proctype.mod

MODULE TProcType;
// Procedure types: alias, procedure-typed variable, assignment of a
// procedure name, and indirect call. Both the named parameter form
// (a, b : INTEGER) and the type-only shorthand (INTEGER) are used.
// Exit 42.
TYPE BinOp = PROCEDURE (a, b : INTEGER) : INTEGER;
TYPE UnOp  = PROCEDURE (INTEGER) : INTEGER;

VAR ExitCode : INTEGER;
VAR f : BinOp;
VAR g : UnOp;

PROCEDURE Add (a, b : INTEGER) : INTEGER;
BEGIN RETURN a + b END Add;

PROCEDURE Neg (x : INTEGER) : INTEGER;
BEGIN RETURN -x END Neg;

BEGIN
  f := Add;
  ExitCode := f(40, 2);              // 42
  g := Neg;
  ExitCode := ExitCode + g(-5) - 5   // 42 + 5 - 5 = 42
END TProcType.