anchor.diff:  CONST: 'const';
   VAR: 'var';
   PROC: 'proc';
  +END_PROC: 'end_p';
   CPROC: 'cproc';
   IMPORT: 'import';
   INCLUDE: 'include';
  
positive.code: STATIC_IF: 'static_if';
  THEN: 'then';
  ELSE: 'else';
  ENDIF: 'endif';
  UNIT: 'unit';
  PLUS: '+';
  MINUS: '-';
  
negative.code: FALSE: 'false';
  ALIAS: 'alias';
  LET: 'let';
  SCOPE_LEAVE: 'scope_leave'; // code block run at leaving scope
  END_SCOPE_LEAVE: 'end_sl';
  
  // literals
  fragment ESC: '\\"' | '\\\\';
  