Markus Böhm wrote:
Hi, I'd like to understand in principle, how monadic I/O actions and combinators (>>=) are translated into imperative C--, to be executed sequentially.
Does sequencing of IO actions mean nesting of C-- functions and passing values/state via additional function parameters?
Is there any material with examples available?
P.S.: Just to understand the magic better. I need it.
Well, the key point of the IO monad is of course that the internals are abstracted away. I'm not sure you will get much understanding out of them. If I am informed correctly, GHC represents IO as newtype IO a = IO ( World -> (# a, World #) ) But World is just a dummy type, it models the execution order as data dependencies so that the optimizer doesn't mess with it. In other word, World is stripped out completely, primitives like putChar are pretty much just compiled down to foreign function calls in C--. There are other possibilities, I believe NHC and YHC represent IO as newtype IO a = IO ( World -> a ) Again, the World argument is just a dummy. Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com