Thank you for your responses.
My algorithm that needs the described function performs
so horribily bad that I understand now the need for CNF :-)
The idea was to write a CYK-style parser for an arbitrary
context-free grammar without transformation to CNF.
To compute derivations for a span of length i
I wanted to iterate over all productions p, counting
the number n of Nonterminals at the right-hand side of p,
computing all lists with n numbers whose sum is i and
split the span accordingly. It works, however, the strings
have to be very, very short *g*
Ciao and Thx,
Steffen
2007/5/22, Jules Bean
Matthew Brecknell wrote:
This seems to work, but presumably only because it's a boxed array, and the construction makes no circular references.
Yes, AIUI the boxed arrays are strict in indices but lazy in values. Therefore they can be used for this kind of memoization trick as long as you're access the elements in 'some sensible order' (that is the calculation dependencies are well-ordered). _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
-- Dipl.-Inform. Steffen Mazanek Institut für Softwaretechnologie Fakultät Informatik Universität der Bundeswehr München 85577 Neubiberg Tel: +49 (0)89 6004-2505 Fax: +49 (0)89 6004-4447 E-Mail: steffen.mazanek@unibw.de