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<html><head><title>Using the NHC.BinArray library</title></head>
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<center><h1>Using the NHC.BinArray library</h1></center>
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This document describes the York BinArray library, a library for
imperative binary arrays which, although it is implemented using the
<a href="Binary.html">Binary</a> library, has an independent interface and
can be used pretty-much without any knowledge of the Binary library at
all. We present this BinArray module as an example of the use of the
Binary library to build higher-level facilities, and would encourage
programmers to write and publish other useful libraries in a similar
manner.
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<h3><a name=binarray>NHC.BinArray library</a></h3>
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<pre>
module NHC.BinArray
( type BinArray
, newBinArray
, intoBinArray
, fromBinArray
, putBinArray
, getBinArray
) where
data BinArray a = ...
newBinArray :: Binary a => Int -> a -> IO (BinArray a)
intoBinArray :: Binary a => BinArray a -> a -> IO Int
fromBinArray :: Binary a => BinArray a -> Int -> IO a
putBinArray :: Binary a => FilePath -> BinArray a -> IO ()
getBinArray :: Binary a => FilePath -> IO (BinArray a)
</pre>
<p>
A <tt>BinArray a</tt> is an imperative (mutable) array that holds values
of type <tt>a</tt> in binary representation. It is implemented using
the Binary library, but as you can see, this is largely hidden from
the programmer. A BinArray can only be written to sequentially. If one
attempts to read a value from an index position which has not yet been
written to (or which is beyond the bounds of the array), a default value
is returned.
<p>
A BinArray can be stored in a file between program runs. Reading and
writing BinArrays to disk is fast. Once a BinArray has been read back
from disk, it can be written to again in the usual way.
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<td><tt>newBinArray n d</tt></td>
<td>gives you a fresh binary array of size <tt>n</tt>,
filled with default value <tt>d</tt>. The binary values are
stored in memory.</td>
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<td><tt>intoBinArray ba x</tt></td>
<td>stuffs the value <tt>x</tt> into the array <tt>ba</tt>
using a binary representation</td>
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<td><tt>fromBinArray ba i</tt></td>
<td>gives you back the value at the <tt>i</tt>'th
position in the array <tt>ba</tt></td>
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<td><tt>putBinArray fn ba</tt></td>
<td>copies the whole array <tt>ba</tt> into a binary file whose name is
<tt>fn</tt></td>
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<td><tt>getBinArray fn</tt></td>
<td>gives you back a binary array read from the file named <tt>fn</tt></td>
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<hr>
<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>
1998.03.26<br>
<a href="http://www.cs.york.ac.uk/fp/">
York Functional Programming Group</a><br>
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