On 2009 Apr 10, at 0:33, Heinrich Apfelmus wrote:
Luke Palmer wrote:
Miguel Mitrofanov wrote:
I'm not sure what you mean by that, but semantically IO is definitely
*not* a state monad. Under any circumstances or any set of assumptions.
Ehm? Why not?
Mainly forkIO. There may be other reasons. loop' :: IO () loop' = putStr "o" >> loop'
are indistinguishable in the
IO a ~ World -> (a, World)
I still don't understand this; we are passing a World and getting a World back, *conceptually* the returned World is modified by putStr. It's not in reality, but we get the same effects if we write to a buffer and observe that buffer with a debugger --- state threading constrains the program to the rules that must be followed for ordered I/O, which is what matters. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH