On Mon, Sep 1, 2008 at 1:00 AM, Don Stewart
I also wonder if we could give a String syntax to the formatting language, using -XOverloadedStrings and the IsString class.
Probably easier with Template Haskell:
ghci -fth Sprintf.hs *Sprintf> :t $(sprintf "Hello %s, showing %S and %S") $(sprintf "Hello %s, showing %S and %S") :: (Show a1, Show a) => [Char] -> a -> a1 -> [Char] *Sprintf> $(sprintf "Hello %s, showing %S and %S") "Don" 1 (5,6) "Hello Don, showing 1 and (5,6)"
Code follows, which could be ported to use the printf/scanf language Oleg defined. -- ryan {-# LANGUAGE TemplateHaskell #-} module Sprintf where import Language.Haskell.TH data SprintfState = SprintfState String (ExpQ -> ExpQ) flush :: SprintfState -> (ExpQ -> ExpQ) flush (SprintfState "" k) = k flush (SprintfState s k) = (\e -> k [| $(litE $ StringL $ reverse s) ++ $e |]) finish :: SprintfState -> ExpQ finish (SprintfState s k) = k (litE $ StringL $ reverse s) addChar :: Char -> SprintfState -> SprintfState addChar c (SprintfState s e) = SprintfState (c:s) e addCode :: ExpQ -> SprintfState -> SprintfState addCode k s = SprintfState "" (\e -> flush s $ [| $k ++ $e |]) sprintf' :: SprintfState -> String -> ExpQ sprintf' k ('%':'S':cs) = [| \x -> $(sprintf' (addCode [| show x |] k) cs) |] sprintf' k ('%':'s':cs) = [| \s -> $(sprintf' (addCode [| s |] k) cs) |] sprintf' k ('%':'%':cs) = sprintf' (addChar '%' k) cs sprintf' k (c:cs) = sprintf' (addChar c k) cs sprintf' k [] = finish k sprintf :: String -> ExpQ sprintf = sprintf' (SprintfState "" id)