186 lines
8.6 KiB
HTML
186 lines
8.6 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head>
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<title>.</title>
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</head><body>
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<p><span class="h1">Working With a Buffer</span>
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<br/><br/>
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RETRO provides words for operating on a linear memory area.
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This can be useful in building strings or custom data
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structures.
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<br/><br/>
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<span class="h2">Namespace</span>
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<br/><br/>
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Words operating on the buffer are kept in the <span class="tt">buffer:</span>
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namespace.
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<br/><br/>
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<span class="h2">Implementation</span>
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<br/><br/>
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A buffer is a linear sequence of memory. The buffer words
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provide a means of incrementally storing and retrieving
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values from it.
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<br/><br/>
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The buffer words keep track of the start and end of the
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buffer. They also ensure that an <span class="tt">ASCII:NULL</span> is written
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after the last value, which make using them for string
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data easy.
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<br/><br/>
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<span class="h2">Limitations</span>
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<br/><br/>
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Only one buffer can be active at a time. RETRO provides a
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<span class="tt">buffer:preserve</span> combinator to allow using a second one
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before returning to the prior one.
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<br/><br/>
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<span class="h2">Set The Active Buffer</span>
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<br/><br/>
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To set a buffer as the active one use <span class="tt">buffer:set</span>. This takes
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an address.
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<br/><br/>
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The buffer will be assumed to be empty. The initial value will
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be set to ASCII:NULL.
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<br/><br/>
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<span class="h2">Add Value</span>
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<br/><br/>
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Use <span class="tt">buffer:add</span> to append a value to the buffer. This takes
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a single value and will also add an ASCII:NULL after the end
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of the buffer.
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<br/><br/>
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<span class="h2">Fetch Last Value</span>
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<br/><br/>
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To return the last value in the buffer you can use <span class="tt">buffer:get</span>.
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This removes the value and sets an ASCII:NULL in the memory
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location the returned value occupied.
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<br/><br/>
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<span class="h2">Get Data About The Buffer</span>
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<br/><br/>
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RETRO provides <span class="tt">buffer:start</span> to get the initial address in
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the buffer, <span class="tt">buffer:end</span> to get the last address (ignoring the
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ASCII:NULL), and <span class="tt">buffer:size</span> to return the number of values
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in the buffer.
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<br/><br/>
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<span class="h2">Reset</span>
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<br/><br/>
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You can reset a buffer to the empty state using <span class="tt">buffer:empty</span>.
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<br/><br/>
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<span class="h2">Example</span>
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<br/><br/>
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To begin, create a memory region to use as a buffer.
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='str'>'Test</span> d:create <span class='num'>#1025</span> allot </span><br/>
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<span class="tt">```</span></span><br/><br/>
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Then you can set this as the current buffer:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='ptr'>&Test</span> buffer:set </span><br/>
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<span class="tt">```</span></span><br/><br/>
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When a buffer is set, the vocabulary sets an internal
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index to the first address in it. This will be
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incremented when you add data and decremented when you
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remove data.
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<br/><br/>
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Let's add some stuff using <span class="tt">buffer:add</span>:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='num'>#100</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#200</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#300</span> buffer:add </span><br/>
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<span class="tt">```</span></span><br/><br/>
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And then retrieve the values:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt">buffer:get n:put nl </span><br/>
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<span class="tt">buffer:get n:put nl </span><br/>
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<span class="tt">buffer:get n:put nl </span><br/>
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<span class="tt">```</span></span><br/><br/>
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You can remove all values using <span class="tt">buffer:empty</span>:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='num'>#100</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#200</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#300</span> buffer:add </span><br/>
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<span class="tt">buffer:empty </span><br/>
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<span class="tt">```</span></span><br/><br/>
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And ask the buffer how many items it contains:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt">buffer:size n:put nl </span><br/>
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<span class="tt"><span class='num'>#100</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#200</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#300</span> buffer:add </span><br/>
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<span class="tt">buffer:size n:put nl </span><br/>
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<span class="tt">buffer:empty </span><br/>
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<span class="tt">```</span></span><br/><br/>
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The other functions are <span class="tt">buffer:start</span>, which returns
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the address of the buffer, <span class="tt">buffer:end</span>, which returns
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the address of the last value, and <span class="tt">buffer:preserve</span>.
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The first is easy to demo:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt">buffer:start Test <span class='prim'>eq?</span> n:put nl </span><br/>
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<span class="tt">```</span></span><br/><br/>
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The last one is useful. Only one buffer is ever active
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at a given time. The <span class="tt">buffer:preserve</span> combinator lets
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you execute a word, saving and restoring the current
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buffer indexes. So the word could assign and use a new
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buffer and this will reset the previous one after
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control returns.
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<br/><br/>
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There are a few notes that need to be considered. The
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preserve combinator saves the start and current index
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but <strong>not</strong> the contents. If the word you call uses the
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same buffer, the contents will remain altered.
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<br/><br/>
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Finally, the buffer words have one interesting trait:
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they store an ASCII NULL after adding each item to the
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buffer. This lets one use them to build strings easily.
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt">Test buffer:set </span><br/>
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<span class="tt"><span class='char'>$h</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$e</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$l</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$l</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$o</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$,</span> buffer:add </span><br/>
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<span class="tt"><span class='num'>#32</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$w</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$o</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$r</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$l</span> buffer:add </span><br/>
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<span class="tt"><span class='char'>$d</span> buffer:add </span><br/>
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<span class="tt">buffer:start s:put nl </span><br/>
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<span class="tt">```</span></span></p>
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</body></html>
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