/usr/share/doc/frown-doc/examples/manual/VarParen.lg is in frown-doc 0.6.2.3-4.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | > module VarParen where
> import Result
>
> newtype Tree = Node [Tree]
> deriving (Show)
>
> %{
>
> Terminal = '(' | ')';
>
> Nonterminal = paren {Tree};
>
> paren {Node []} : ;
> {Node (x : xs)} | paren {x}, '(', paren {Node xs}, ')';
>
> }%
>
> frown ts = fail "syntax error"
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