An ALLCOT program

An ALLCOT program consists of a sequence of definitions, the last one being the definition of a function called main, followed by a call to this function. Executing this program means executing this call. An example of such program is given below.

Monoid: Category == with {
  print: % -> ();
  times: (%, %) -> %;
  one: () -> %;
  equal?: (%, %) -> Boolean;
}
MonoidOfZ: Category ==  Monoid with {
  convert: Integer -> %;
}
OddNumbers: MonoidOfZ == add {
  attrib(n: Integer);
  convert(x: Integer): % == 
    if (x rem 2 = 1) then attrib(x) else error;
  print(x: %): () == print (x.n);
  times(x: %, y: %): % == attrib((x.n) * (y.n));
  one(): % == convert(1);
  equal?(x: %, y: %): Boolean == (x.n) = (y.n); 
}
WordMonoid: Category == Monoid with {
  word: String -> %;
}
Word: WordMonoid == add {
  attrib(st: String, le: Integer);
  word(x: String): % == attrib(x, length(x));
  print(x: %): () == print (x.st);
  times(x: %, y: %): % == {
    z: String := concat(x.st,y.st);
    l: Integer := x.le + y.le;
    attrib(z,l);
  }
  one(): % == word(empty(),0);
  equal?(x: %, y: %): Boolean == {
    if (x.le ~= y.le) then return false;
    equal?(x.st,y.st);
  }
}
main(): () == {
  x: Word := word("Hello ");
  y: Word := word("Mars.");
  xy: Word := times(x,y);
  print(xy);
}
main();

Up to the magic function attrib, the program above could be a fragment of an ALDOR program. It declares three categories (or interfaces) and two domains (or classes). If you are an ALDOR user, you could be surprised by this attrib function: the goal here is to keep the grammar, the type checking and the translation simple!

Observe also that the above program relies on three built-in domains, namely Boolean, String and Integer.