Using the combinators at: http://www.cs.uu.nl/groups/ST/Software/UU_Parsing the problem is solved by (see also the file demo.hs there): pLetter = pAnyOf "abcdefghijklmnopqrstuvwxyz" pString = pList pLetter pAll elems = foldr ((*>) . pSym) (pSucceed []) elems pRoot keys = pString <* pPacked (pSym '<') (pSym '>') (foldr (<|>) pFail (map pAll keys)) <* pString Doaitse Swierstra PS: small modifications may be needed depending on what you want to do with the part after the keyword At 01:24 -0500 2/8/00, Christopher Sharpe wrote:
Hello,
Thanks to those who pointed out that my previous function p was not tail recursive. I think "exclude" (below) is. It seems to work on large files, although on a 160K file garbage collection fails to get enough space.
What I am trying to do is find, in input such as an HTML file, like "ab<table>c", the string before the keyword such as "table". So I try the keyword parsers (in the list "ps" below) at each point in the input, and add the character to my answer if all the parsers fail. Something like a Boyer-Moore string search might be used to, though that would add complexity. I couldn't find such an algorithm in any Hugs library.
---------------------------- program -----------------------------
import ParseLib
exclude ans parsers = P (\inp -> case inp of [] -> [(reverse ans,"")] (c:cs) -> case papply try inp of [(_,remaining)] -> [(reverse ans,remaining)] [] -> papply (exclude (c:ans) parsers) cs ) where try = commonSubstring >> foldr1 (+++) parsers
test = papply (exclude "" ps) "ab<table>c"
commonSubstring = string "<"
ps = [string "table>",string "/table>" ] Content-Type: Haskell; name="ww.hs" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="ww.hs"
Attachment converted: Doaitse:ww.hs 2 (????/----) (00006585)
-- __________________________________________________________________________ S. Doaitse Swierstra, Department of Computer Science, Utrecht University P.O.Box 80.089, 3508 TB UTRECHT, the Netherlands Mail: mailto:doaitse@cs.uu.nl WWW: http://www.cs.uu.nl/ PGP Public Key: http://www.cs.uu.nl/people/doaitse/ tel: +31 (30) 253 3962, fax: +31 (30) 2513791 __________________________________________________________________________