[PD] Haskell external for Pd (Was: Re: Thanks for you patience.)

Claude Heiland-Allen claudiusmaximus at goto10.org
Wed Mar 7 00:30:53 CET 2007

Hi David, and all,

David F. Place wrote:
> I have a strong leaning toward recursive solutions as I have 
> been programming exclusively in Haskell for years.

You may be interested in [hsext], an external I'm working on that allows 
you to create Pd objects in Haskell.

You can check out the current latest and greatest version from SVN, be 
warned that it's under development and the API will probably change 
quite a bit before I get it how I want it:

svn co https://devel.goto10.org/svn/maximus/hsext hsext

If you need a "known working" version, revision 213 (the current version 
as of writing this email) is the one for you:

svn co -r 213 https://devel.goto10.org/svn/maximus/hsext hsext

I plan to change the API to better match Pd's way of doing things (and 
fix some design mistakes on my part), which should hopefully make the 
Haskell code clearer and more future-proof too, while also hiding some 
of Pd's API pains.


pd-0.39-2, pd-0.40-2, older versions might work, but I haven't tried.

(ghc-6.6 + hs-plugins-1.0-rc0 = pain, you have been warned)

Simple example (as provided in revision 213):

-- swap two messages (not only individual floats...)

module Swap where

import Data.IORef
import PureData

creator :: Creator
creator args = do
   bang <- gensym "bang"
   state <- newIORef (bang, [])
   return (Just Instance{iInlets = 2, iOutlets = 2, iMethod = inlet state})

inlet state outlet 0 s m = do
   (rs,rm) <- readIORef state
   outlet 1 s m
   outlet 0 rs rm
   return ()

inlet state outlet 1 s m = do
   writeIORef state (s,m)
   return ()

-- end of example

Complex example (screenshot, the Haskell code generates vectors):



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