foldExpr::(Integer -> b) -> (b -> b -> b) -> (b -> b -> b) -> (String -> b) -> (String -> b -> b -> b) -> Exp -> b
foldExpr fcte fsuma fmult fvar flet expre = case expre of
											Cte n -> fcte n
											Suma exp1 exp2 -> fsuma (recu exp1) (recu exp2)
											Mult exp1 exp2 -> fmult (recu exp1) (recu exp2)
											Var str -> fvar str
											Let str exp1 exp2 -> flet str (recu exp1) (recu exp2)
											where recu = foldExpr fcte fsuma fmult fvar flet