Defining a real programming language

Real programming brings up more challenges than the simple calc language from the previous chapter. To have a look at the details, we will be using a tiny subset of Modula-2 in this and the following chapters. Modula-2 is well-designed and optionally supports generics and object-orientated programming (OOP). However, we are not going to create a complete Modula-2 compiler in this book. Therefore, we will call the subset tinylang.

Let’s begin with an example of what a program in tinylang looks like. The following function computes the greatest common divisor using the Euclidean algorithm:

MODULE Gcd;
PROCEDURE GCD(a, b: INTEGER) : INTEGER;
VAR t: INTEGER;
BEGIN
  IF b = 0 THEN
    RETURN a;
  END;
  WHILE b # 0 DO
    t := a MOD b;
    a := b;
    b := t;
  END;
  RETURN a;
END GCD;
END Gcd.

Now that we...