On Oct 15, 2007, at 13:32 , Peter Verswyvelen wrote:
[EMAIL PROTECTED] wrote:
Yes, *different approach*. So, there *are* differences.
Compilers, anyway,
are special applications. I wanted to see - responding to Brandon
- a
"normal" Haskell program, which does IO without monads, that't all.
The problem is then when you hide something, you hide. It is
possible to
superpose a kind of monadic framework on unique worlds, files,
etc. in
Clean, but the reverse operation goes beyond my horizons.
Some examples, anybody?
Ah yes, I see what you mean now. I have no idea, I guess only
unsafePerformIO will allow you to do something like that... But
that will completely break referential transparency. But I really
don't know. What do the experts have to say?
Use the source of unsafePerformIO as an example of how to write code
which passes around RealWorld explicitly, but without unencapsulating
it like unsafePerformIO does.
The main problem here, I think, is that because all the GHC runtime's
functions that interact with RealWorld (aside from unsafe*IO) are
themselves only exported wrapped up in IO, you can't (as far as I
know) get at the lower level internal (e.g.) putStrLn' :: RealWorld -
> String -> (# RealWorld,() #) to do I/O in a direct/explicit/non-
monadic style. In theory, one could export those and use them directly.
(Actually, as a practical matter, IIRC GHC "knows about" RealWorld
and removes all of it when generating cmm code once it's done the job
of sequencing Haskell evaluation; I'm not sure how well that would
work if you wrote I/O in direct/explicit style. unsafePerformIO
doesn't really count for that because it removes the RealWorld itself.)
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon university KF8NH
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