PPL SOURCE SYNTAX

  Each line of a PPL source file may contain none, one, some or all
  of the following sections:

  [KEYWORD ][EXPR|VAR][,EXPR|VAR][;|'][COMMENT TEXT]

  KEYWORD - A PPL statement used to accomplish some task.
  EXPR    - A PPL expressioin which may contain VARs, CONSTs,
            and/or FUNCs.
  VAR     - A PPL variable with optional array subscript.
  CONST   - A PPL constant.
  FUNC    - A PPL function that returns a value.
  ;       - Used to start a comment.  Ignored by the compiler.
  '       - Used to start a comment.  Ignored by the compiler.
  COMMENT - Comment text following the ; or '.
            Ignored by the compiler.

  If a line is blank or contains only a comment, it is skipped.
  If it contains a KEYWORD, that line is compiled into a tokenized format.
  If it doesn't contain a KEYWORD but some argument, it is assumed to
  be an assignement statement (LET).

  Note: ^M should be used to pass a carrage return to the PCBoard
        command processor.