trans :: Expression -> String
trans = trans_E []

trans_E :: Tab -> Expression -> String
trans_E varDefs ex = case ex of
  Val valOfNum -> "top++; S[top] = " ++ (show valOfNum :: Int)
  Idf valName -> "top++; S[top] = L[" ++ (show (lookup valName varDefs)) ++ "];"
  Binary lhs op rhs -> case op of
    Plus -> (trans varDefs lhs) ++ (trans varDefs rhs) ++ "top--;S[top]=S[top]+S[top+1];"
    Minus -> (trans varDefs lhs) ++ (trans varDefs rhs) ++ "top--;S[top]=S[top]-S[top+1];"
    Times -> (trans varDefs lhs) ++ (trans varDefs rhs) ++ "top--;S[top]=S[top]*S[top+1];"
    Div -> (trans varDefs lhs) ++ (trans varDefs rhs) ++ "top--;S[top]=S[top]/S[top+1];"
  Let valName valExpr inExpr -> (trans varDefs valExpr) ++ "L["++(show (lookup valName varDefs))++"]=S[top]; top--,"++(trans (valName,(lookup valName varDefs)):varDefs inExpr)