Problem Statement

Create and display the sequence of binary digits for a given   non-negative integer. The results can be achieved using built-in radix functions within the language   (if these are available),   or alternatively a user defined function can be used. The output produced should consist just of the binary digits of each number followed by a   newline. There should be no other whitespace, radix or sign markers in the produced output, and leading zeros should not appear in the results.

Let's start with the solution:

MODULE BinaryDigits;
IMPORT  Out;
 
  PROCEDURE OutBin(x: INTEGER);
  BEGIN
    IF x > 1 THEN OutBin(x DIV 2) END;
    Out.Int(x MOD 2, 1);
  END OutBin;
 
 
BEGIN
  OutBin(0); Out.Ln;
  OutBin(1); Out.Ln;
  OutBin(2); Out.Ln;
  OutBin(3); Out.Ln;
  OutBin(42); Out.Ln;
END BinaryDigits.