[Haskell-cafe] Re: Referential Transparency and Monads

[Achim Schneider]

Jonathan Cast <jonathanccast at fastmail.fm> wrote:

> On Fri, 2009-04-10 at 07:29 +0400, Miguel Mitrofanov wrote:
> > On 10 Apr 2009, at 06:30, Jonathan Cast wrote:
> > >  do
> > >     s <- readFile "/my_file"
> > >     writeFile "/my_file" "Hello, world!\n"
> > >     threadDelay 10000 -- If you don't like threadDelay, just  
> > > substitute forcing
> > >                       -- an expensive thunk here
> > >     writeFile "/my_file" s
> > >
> > > As a function from initial state to final state, this program is
> > > just the identity;
> > 
> > No, since world state includes the user state itself, not just
> > files contents.
> 
> My programs are passing me around inside a state token?
> 
Sure.

http://en.wikipedia.org/wiki/File:8-cell.gif

Inside and outside become quite mindboggling when dealing with more
dimensions than you expect...

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