%%% $Id: Restrictions.sdf 17765 2006-02-13 12:54:52Z jurgenv $
               
module languages/sdf2/syntax/Restrictions

imports languages/sdf2/syntax/CC

exports
  sorts Lookahead Lookaheads Restriction Restrictions

  context-free syntax
    CharClass                          -> Lookahead  {cons("char-class")}
    head:CharClass "." tail:Lookaheads -> Lookahead  {cons("seq")}

    Lookahead                                -> Lookaheads  {cons("single")}
    "left":Lookaheads "|" "right":Lookaheads -> Lookaheads  {cons("alt"),right}
    "(" Lookaheads ")"                       -> Lookaheads  {bracket}
    "[[" list:{Lookahead ","}* "]]"          -> Lookaheads  {cons("list")}

    Symbols "-/-" Lookaheads -> Restriction  {cons("follow")}

    list:Restriction* -> Restrictions

    "restrictions" Restrictions -> Grammar  {cons("restrictions")}

    "reject" -> Attribute  {cons("reject")}
    "prefer" -> Attribute  {cons("prefer")}
    "avoid"  -> Attribute  {cons("avoid")}

  context-free priorities    
    CharClass "." Lookaheads    -> Lookahead >
    Lookaheads "|" Lookaheads   -> Lookaheads
