File: Paren.lg

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{-

	frown Paren.lg

Try


Left-recursive definition.	

Expr                          :  Expr, '(', Expr, ')';
                              |  ;

-}

> module Paren
> where
>
> data Tree                     =  Node [Tree]
>                                  deriving (Show)
>
> empty                         =  Node []
> join t (Node us)              =  Node (t : us)
>
> type Terminal                 =  Char
>
> type Result                   =  []
>
> %{
>
> Terminal                      =  '(' | ')';
>
> Nonterminal                   =  expr {Tree};
>
> expr {join t u}               :  expr {t}, '(', expr {u}, ')';
>      {empty}                  |  ;
>
> }%
>
> frown ts                      =  fail "syntax error"