Hello everybody, I checked the topics in Haskell-Cafe about prefix/infix operators but I did not find them. Now I bring my questions to here to ask you. 1) I have a Common-Lisp code representing an expression result as follows ((MPLUS SIMP) ((MTIMES SIMP) ((RAT SIMP) 1 2) ((MEXPT SIMP) $X 2)) ((MTIMES SIMP) ((RAT SIMP) 1 3) ((MEXPT SIMP) $X 3))) 2) I attempted to change it to mathematics operators, replacing MPLUS SIMP -> + MEQUAL SIMP -> = RAT SIMP -> / MEXPT SIMP -> ^ translate :: String -> String translate [] = [] translate ('(':'M':'P':'L':'U':'S':' ':'S':'I':'M':'P':')':xs) = "(+)" ++ translate xs translate ('(':'M':'T':'I':'M':'E':'S':' ' :'S':'I':'M':'P':')':xs) = "(*)" ++ translate xs translate ('(':'M':'E':'Q':'U':'A':'L':' ' :'S':'I':'M':'P':')':xs) = "(=)" ++ translate xs translate ('(':'R':'A':'T':' ':'S':'I':'M':'P':')':xs) = "(/)" ++ translate xs translate ('(':'M':'L':'I':'S':'T':' ':'S':'I':'M':'P':')':xs) = "([])" ++ translate xs translate ('(':'M':'E':'X':'P':'T':' ':'S':'I':'M':'P':')':xs) = "(^)" ++ translate xs translate ('$':'X':xs) = "x" ++ translate xs translate ('$':'Y':xs) = "y" ++ translate xs translate (x:xs) = x:translate xs 3) And NOW I want to transfer from prefix operator into infix operator, for example: From ((+) ((*) ((/) 1 2) ((^) x 2)) ((*) ((/) 1 3) ((^) x 3))) in to the expression: 1/2*x^2+1/3*x^3 I try to figure out it, but this time it is not successfully. If you are familiar with that, please share with me. Many thanks to all. S.