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<center><h1>The NHC.PackedString library in nhc98</h1></center>
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This document sketches the PackedString library in nhc98. It is
closely based on the non-standard PackedString library in hbc.
It provides a more space-efficient representation of 8-bit character
strings than the standard list-of-characters representation.
A PackedString containing n characters occupies at most (n`div`4)+2
words of heap memory, whereas a fully evaluated ordinary string
occupies at least (n*2)+2 words. The price to pay is that the contents
of a PackedString is always fully evaluated, whereas an ordinary
String may be lazy. Thus, an unevaluated String can actually take
less space than an evaluated PackedString.
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<h3>The NHC.PackedString library</h3>
<pre>
module NHC.PackedString
( PackedString -- abstract, instance of Eq, Ord, Show, Read
, packString -- :: String -> PackedString
, unpackPS -- :: PackedString -> String
, cons -- :: Char -> PackedString -> PackedString
, nil -- :: PackedString
, head -- :: PackedString -> Char
, tail -- :: PackedString -> PackedString
, append -- :: PackedString -> PackedString -> PackedString
, break -- :: (Char->Bool) -> PackedString -> (PackedString, PackedString)
, concat -- :: [PackedString] -> PackedString
, drop -- :: Int -> PackedString -> PackedString
, dropWhile -- :: (Char->Bool) -> PackedString -> PackedString
, filter -- :: (Char->Bool) -> PackedString -> PackedString
, foldl -- :: (a->Char->a) -> a -> PackedString -> a
, foldr -- :: (Char->a->a) -> a -> PackedString -> a
, index -- :: PackedString -> Int -> Char
, length -- :: PackedString -> Int
, lines -- :: PackedString -> [PackedString]
, map -- :: (Char->Char) -> PackedString -> PackedString
, null -- :: PackedString -> Bool
, reverse -- :: PackedString -> PackedString
, span -- :: (Char->Bool) -> PackedString -> (PackedString, PackedString)
, splitAt -- :: Int -> PackedString -> (PackedString, PackedString)
, substr -- :: PackedString -> Int -> Int -> PackedString
, take -- :: Int -> PackedString -> PackedString
, takeWhile -- :: (Char->Bool) -> PackedString -> PackedString
, unlines -- :: [PackedString] -> PackedString
, unwords -- :: [PackedString] -> PackedString
, words -- PackedString -> [PackedString]
)
where
import Prelude hiding (append,break,concat,cons,drop,dropWhile,
filter,foldl,foldr,head,Ix(..),
length,lines,Functor(..),map,nil,null,
reverse,span,splitAt,substr,tail,take,
takeWhile,unlines,unwords,words)
</pre>
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<p>
The latest updates to these pages are available on the WWW from
<a href="http://www.cs.york.ac.uk/fp/nhc98/">
<tt>http://www.cs.york.ac.uk/fp/nhc98/</tt></a>
<p>
2001.11.27<br>
<a href="http://www.cs.york.ac.uk/fp/">
York Functional Programming Group</a><br>
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