5 comments on “Riddle me this”

1. sclv says:

   2009-09-25 at 15:51

   this is a terrible hack, but no more of a hack than printf itself:

   test :: (HPrintfType r, NoOp r) => Bool -> Handle -> String -> r
   test b = if b then hPrintf
   else nopr

   class NoOp a where
   nopr :: a

   instance NoOp (IO a) where
   nopr = return undefined

   instance (NoOp r) => NoOp (a -> r) where
   nopr = const $ nopr

   don’t have an answer for the second bit at the moment tho.
2. brian says:

   2009-09-26 at 00:09

   Don’t forget package ‘xformat’.
3. Saizan says:

   2009-09-26 at 00:38

   I got a solution requiring more extensions but that it looks more general, here’s the paste:
   http://hpaste.org/fastcgi/hpaste.fcgi/view?id=9857

   The types, especially those inferred like in test, aren’t so pretty but not horrible either.
4. Bryan O'Sullivan says:

   2009-09-26 at 12:40

   Saizan: Wow, that’s impressive. Type signatures longer than the code they describe? Eeek!
5. Saizan says:

   2009-09-26 at 12:46

   well, the typeclass system is what’s doing most of the work

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1. Text.Printf and monad transformers « Communicating Haskell Processes says:

   2009-11-06 at 08:35

   [...] little while ago, Bryan O’Sullivan was developing his Criterion benchmark suite, and had trouble with using the Text.Printf module in a monad transformer on top of IO. I thought I knew how to solve this, but my first idea didn’t work — and nor did my [...]