On May 27, 2009, at 1:01 AM, Ahn, Ki Yung wrote:
By the way, did Curry solved the problem of how to deal with IO and
backtracking issues? (where and where not should IO happen kind of
a thing)
Curry uses the IO monad to specify where IO actions may happen. Non-
determinism is not excluded statically from IO actions but usually
leads to a run-time error (see Section 7.1 of [1]). For example the
Curry systems PAKCS [2] and MCC [3] show the following behaviour (the
infix operator (?) denotes non-deterministic choice):
$ pakcs
Prelude> print (1?2)
1
2
ERROR: non-determinism in I/O actions occurred!
Prelude> :q
$ cyi
Prelude> print (1?2)
Error: cannot duplicate the world
Prelude> :q
In order to use non-deterministic operations in an IO context, their
results need to be *encapsulated*, i.e., collected in a data structure
(e.g. a list). See [4,5] for recent research on encapsulated search.
The Curry System KiCS [6] uses encapsulated search implicitly in IO
operations and uses the first result if there is one and only yields
an error otherwise:
$ kicsi
Prelude> print (1?2)
1
Prelude> print (1=:=2)
non-exhaustive patterns in function Prelude._case_1
<interactive>: program error
Prelude> :q
Cheers,
Sebastian
[1]: http://www.informatik.uni-kiel.de/~curry/report.html
[2]: http://www.informatik.uni-kiel.de/~pakcs/
[3]: http://danae.uni-muenster.de/~lux/curry/
[4]: http://www.informatik.uni-kiel.de/~mh/papers/JFLP04_findall.html
[5]: Computing with subspaces,
http://web.cecs.pdx.edu/~antoy/homepage/publications.html
[6]: http://www.informatik.uni-kiel.de/prog/mitarbeiter/bernd-brassel/projects/
--
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
