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.)