Grammar demo;
Lexer
  letter = 'a'..'z';
  digit = '0'..'9';
  identifier = letter (letter | digit)*;
  comma = ',';
  blank = (' ' | #9 | #10 | #13)+;
  if = 'if';
  else = 'else';
Parser
  Ignored
    blank;
  p = t*;
  t = identifier | comma | if | else;