Re: [Haskell-beginners] ODP: howto Pipe

then I just need to do a forever loop and use this type data to keep the C internal state.

what's worring me is that I have a sort of internal state but this is not expressed anywhere in the type system...

You can use (StateT IO) instead of plain IO in the pipe to pass that data around. There are functions for working with StateT (and other transformer) pipes in Pipes.Lift module: https://hackage.haskell.org/package/pipes-4.1.8/docs/Pipes-Lift.html#g:5 Other than that, having to worry about state kept in the C part of a Haskell program is often a pain in general, unfortunately. Perhaps you could take some hints from https://hackage.haskell.org/package/GPipe for example, but I have no idea if that's going to be of any help.

I get a segfault when I do a big number of coputation ???

The only change is from Pipes.print to Pipes.drain? This is weird, maybe you'd have better luck asking on Pipes mailing list: https://groups.google.com/forum/?fromgroups#!forum/haskell-pipes ( mailto:haskell-pipes@googlegroups.com ) Best regards, Marcin Mrotek