Hi,

   Can anyone explain how to turn the code from infix to Prefix. I want to include a let statement below. I not sure of how prefix  works.

 

expr :: Parser Expr
expr = buildExpressionParser table factor
   <?> "expression"

table :: [[Operator Char st Expr]]
table = [[op "*" Mul AssocLeft, op "/" Div AssocLeft]
       ,[op "+" Add AssocLeft, op "-" Sub AssocLeft]
       ]
 where
   op s f assoc
      = Infix (do{ string s; return f}) assoc

factor :: Parser Expr
factor = do{ char '('
          ; x <- expr
          ; char ')'
          ; return x
          }
     <|> number
     <?> "simple expression"

number :: Parser Expr
number = do{ ds <- many1 alphaNum
          ; return (Val $ read ds)
          }
    

John