Classroom Object Oriented Language - Programming language

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Classroom Object Oriented Language, aka Classroom Object Oriented Language, is a programming language created in 1996 by Alexander Aiken.

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Cool, an acronym for Classroom Object Oriented Language, is a computer programming language designed by Alexander Aiken for use in an undergraduate compiler course project. While small enough for a one term project, Cool still has many of the features of modern programming languages, including objects, automatic memory management, strong static typing and simple reflection. The reference Cool compiler is written in C++, built fully on the public domain tools. Read more on Wikipedia...

Classroom Object Oriented Language Wikipedia page
There are at least 102 Classroom Object Oriented Language repos on GitHub
Classroom Object Oriented Language first developed in Stanford University
file extensions for Classroom Object Oriented Language include cl
The Google BigQuery Public Dataset GitHub snapshot shows 56 users using Classroom Object Oriented Language in 57 repos on GitHub
GitHub supports syntax highlighting for Classroom Object Oriented Language
See also: (7 related languages)CLIPS, Sather, Java, ML, Pascal, OCaml, MIPS architecture

Example from hello-world:

class Main inherits IO {
   main(): Object {
	out_string("Hello World.\n")
   };
};

Example from Linguist:

(* This simple example of a list class is adapted from an example in the
   Cool distribution. *)

class List {
   isNil() : Bool { true };
   head()  : Int { { abort(); 0; } };
   tail()  : List { { abort(); self; } };
   cons(i : Int) : List {
      (new Cons).init(i, self)
   };
};

class Cons inherits List {
   car : Int;	-- The element in this list cell
   cdr : List;	-- The rest of the list
   isNil() : Bool { false };
   head()  : Int { car };
   tail()  : List { cdr };
   init(i : Int, rest : List) : List {
      {
	 car <- i;
	 cdr <- rest;
	 self;
      }
   };
};

Example from Wikipedia:

class Main inherits IO {
  main(): Object {{
    out_string("Enter an integer greater-than or equal-to 0: ");

    let input: Int <- in_int() in
      if input < 0 then
        out_string("ERROR: Number must be greater-than or equal-to 0\n")
      else {
        out_string("The factorial of ").out_int(input);
        out_string(" is ").out_int(factorial(input));
        out_string("\n");
      }
      fi;
  }};

  factorial(num: Int): Int {
    if num = 0 then 1 else num * factorial(num - 1) fi
  };
};