anchor.diff:  -------------------
   
   This implementation of BASIC tokenizes the program text and then parses the tokens.
  +When tokenizing, BASIC builds the longest legal token from available text.
   This can lead to some problems, when legal constructs can be confused for keywords.
   
   For example:
  
positive.code: 	50 NEXT I
  	99 END
  
  The underscore stops the tokenizer and forces it to accept S as a variable and then procede with TOP which will be tokenized as 'TO' and P (as there is no 'TOP' keyword).
  
  Inconsistencies in Ahl's various BASIC interpreters
  ---------------------------------------------------
  
negative.code: Lists the current program on the screen, adjusting the spacing between keywords, variable names, and constants.
  
  Syntax:	PRETTY [line specification]
  
  The line specification is the same as the line specification for the LIST command.
  
  TOKENS
  ~~~~~~
  
  Lists the current program and for each line displays the tokens identified on that line.
  
  Syntax: TOKENS [line specification]
  
  The line specification is the same as the line specification for the LIST command.
  
  