Parsing with parsec - what goes down

ruleHashSubscriptBraces = do
    between start end subscript
    where
    start       = symbol "{"
    end         = char   '}'

    -- try out subscriptExp, but it's okay if it fails
    subscript   = option id subscriptExp

    subscriptExp = do
        exp <- ruleExpression
        return $ \x -> Syn "{}" [x, exp]

• id ?
• \x -> Syn "{}" [x, exp] ????