Hello Jon, Wednesday, April 22, 2009, 1:54:58 PM, you wrote:
Does anyone have any comments on the following criticism of some difficulties with FFI, including IO, in Haskell:
http://groups.google.com/group/comp.lang.functional/msg/6d650c086b2c8a49?hl=...
In particular, is it not always possible to write IO libraries safely in Haskell?
i think that this letter is true on factual part but he exaggerate this problem 1) you can develop any pure-haskell imperative library with safe (no global state) interface and implementation. well, you can do the same with any other language too :) 2) if you are going to hardware level, it usually has von Neumann architecture, i.e. global state. so when providing some service to application, you have to deal with global state at some level. if it doesn't handled at C level (in his example, MVar may be maintained at C side), you need to to this at Haskell level 3) haskell language still doesn't provide features to create global variables, although it was proposed to add syntax he uses: globalLock <- newMVar False -- the same as globalLock = unsafePerformIO (newMVar False) -- but with guarantees of no sharing so we use unsafePerformIO hack instead that's all. if we sometimes deal with global-state C libraries, we may need to use global vars too. anyway, at some level (be it C or Haskell) we need to create safe interface too unsafe von Neumann hardware -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com