Hi, I was watching Rich Hickey's presentations on transducers and decided to implement something like it for foldl folds, as an exercise.
The repo is here: https://github.com/danidiaz/foldl-transduce import qualified Control.Foldl as L import Control.Foldl.Transduce import Control.Foldl.Transduce.Text The main types are type Transduction a b = forall x. Fold b x -> Fold a x data Transducer i o r = forall x. Transducer (x -> i -> (x,[o])) x (x -> (r,[o])) A Transducer is like a Fold that can emit output downstream. A Transducer can be applied to a Fold with the "transduce" function: transduce :: Transducer i o r -> Transduction i o A very simple Transducer is "surround" that adds a prefix and a suffix to the stream of data coming to a Fold: >>> L.fold (transduce (surround "prefix" "suffix") L.list) "middle" "prefixmiddlesuffix" Then there's also decoding transducers: >>> L.fold (transduce utf8lenient L.list) (map fromString ["decode","this"]) ["decode","this"] And also transducer analogues of some functions from pipes-group (they're less powerful though, in that they force you to treat every group the same way): >>> L.fold (groups (chunksOf 2) (transduce (surround [] [0])) L.list) [1..7] [1,2,0,3,4,0,5,6,0,7,0] The existence of pipes makes transducers a bit superflous I suppose. Anyway, once I add some tests and iron out the (very likely) space leaks, I was thinking of putting this on Hackage as foldl-transduce (if Gabriel doesn't mind, I don't want to "name squat" on the foldl-* namespace.) Any comments or bug reports welcome! -- You received this message because you are subscribed to the Google Groups "Haskell Pipes" group. To unsubscribe from this group and stop receiving emails from it, send an email to haskell-pipes+unsubscr...@googlegroups.com. To post to this group, send email to haskell-pipes@googlegroups.com.
