Peter Verswyvelen writes, about non-monadic IO, after the posting of Brandon S. Allbery, who reacted to my claim that IO Monad is unavoidable:
Not really true; it's just much more painful. You just e.g. explicitly do what the ghc library's implementation of IO does: construct a chain of functions with an opaque (and optionally(?) existential to enforce the opacity) "RealWorld" type which is passed as state from one invocation to the next, with the "top level" application partially applied.
P.V.:
Yes indeed, Concurrent Clean actually just passes around the "world" object in "direct/explicit style" but uses uniquness typing to make sure nothing happens that would violate the nice FP paradigm (mainly referential transparency?). That is, I think it's like that :)
Well, I think I am one of not-so-numerous people on this list who use Clean. (After all, it is the competitor... We might forget about the buzzword "Concurrent"...) So, I know about unique *World, *FileSystem, *File, etc., I have used it for graphics and for generation of sound. But I didn't find a way to use *really* this awful "State# RealWorld" in Haskell! Somebody can show me some working examples? Jerzy Karczmarczuk