Many happy returns

ruleHashSubscriptBraces :: RuleParser (Exp -> Exp)
ruleHashSubscriptBraces = do
    between (symbol "{") (char '}') $ option id $ do
        exp <- ruleExpression; return $ \x -> Syn "{}" [x, exp]

• The return value of ruleHashSubscriptBraces is (Exp ->Exp)
• That is, a function taking an Exp and returning an Exp
• Most parser functions return an Exp

• This one returns a closure