154 lines
9.6 KiB
HTML
154 lines
9.6 KiB
HTML
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<title>doc/book/techniques/arrays</title>
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<p><span class="h1">Working With Arrays</span>
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<br/><br/>
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RETRO offers a number of words for operating on statically sized
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arrays.
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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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The words operating on arrays are kept in an <span class="tt">a:</span> namespace.
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<br/><br/>
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<span class="h2">Creating Arrays</span>
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<br/><br/>
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The easiest way to create an array is to wrap the values in a
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<span class="tt">{</span> and <span class="tt">}</span> pair:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#4</span> <span class='imm'>}</span> </span><br/>
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<span class="tt"><span class='imm'>{</span> <span class='str'>'this</span> <span class='str'>'is</span> <span class='str'>'an</span> <span class='str'>'array</span> <span class='str'>'of</span> <span class='str'>'strings</span> <span class='imm'>}</span> </span><br/>
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<span class="tt"><span class='imm'>{</span> <span class='str'>'this</span> <span class='str'>'is</span> <span class='str'>'a</span> <span class='str'>'mixed</span> <span class='str'>'array</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='imm'>}</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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You can also make an array from a quotation which returns
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values and the number of values to store in the a:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>[</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#3</span> <span class='imm'>]</span> a:counted-results </span><br/>
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<span class="tt"><span class='imm'>[</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#3</span> <span class='imm'>]</span> a:make </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Accessing Elements</span>
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<br/><br/>
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You can access a specific value with <span class="tt">a:th</span> and <span class="tt">fetch</span> or
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<span class="tt">store</span>:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#4</span> <span class='imm'>}</span> <span class='num'>#3</span> a:th <span class='prim'>fetch</span> </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Find The Length</span>
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<br/><br/>
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Use <span class="tt">a:length</span> to find the size of the array.
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#4</span> <span class='imm'>}</span> a:length </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Duplicate</span>
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<br/><br/>
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Use <span class="tt">a:dup</span> to make a copy of an a:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#4</span> <span class='imm'>}</span> a:dup </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Filtering</span>
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<br/><br/>
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RETRO provides <span class="tt">a:filter</span> which extracts matching values
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from an array. This is used like:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='num'>#4</span> <span class='num'>#5</span> <span class='num'>#6</span> <span class='num'>#7</span> <span class='num'>#8</span> <span class='imm'>}</span> <span class='imm'>[</span> n:even? <span class='imm'>]</span> a:filter </span><br/>
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<span class="tt">```</span></span><br/><br/>
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The quote will be passed each value in the array and should
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return TRUE or FALSE. Values that lead to TRUE will be collected
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into a new array.
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<br/><br/>
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<span class="h2">Mapping</span>
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<br/><br/>
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<span class="tt">a:map</span> applies a quotation to each item in an array and
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constructs a new array from the returned values.
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<br/><br/>
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Example:
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='imm'>}</span> <span class='imm'>[</span> <span class='num'>#10</span> <span class='prim'>*</span> <span class='imm'>]</span> a:map </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Reduce</span>
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<br/><br/>
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<span class="tt">a:reduce</span> takes an array, a starting value, and a quote. It
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executes the quote once for each item in the array, passing the
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item and the value to the quote. The quote should consume both
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and return a new value.
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<br/><br/>
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<span class='codeblock'><span class="tt">```</span><br/><span class="tt"><span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='imm'>}</span> <span class='num'>#0</span> <span class='imm'>[</span> <span class='prim'>+</span> <span class='imm'>]</span> a:reduce </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Search</span>
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<br/><br/>
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RETRO provides <span class="tt">a:contains?</span> and <span class="tt">a:contains/string?</span>
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to search an array for a value (either a number or string) and
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return either TRUE or FALSE.
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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> <span class='imm'>{</span> <span class='num'>#1</span> <span class='num'>#2</span> <span class='num'>#3</span> <span class='imm'>}</span> a:contains? </span><br/>
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<span class="tt"><span class='str'>'test</span> <span class='imm'>{</span> <span class='str'>'abc</span> <span class='str'>'def</span> <span class='str'>'test</span> <span class='str'>'ghi</span> <span class='imm'>}</span> a:contains/string? </span><br/>
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<span class="tt">```</span></span><br/><br/>
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<span class="h2">Implementation</span>
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<br/><br/>
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In memory, an array is a count followed by the values. As an
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example, if you have an array:
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<br/><br/>
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<tt class='indentedcode'>{ #10 #20 #30 }</tt>
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<br/><br/>
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In memory this would be setup as:
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<br/><br/>
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<tt class='indentedcode'>| Offset | Value |</tt>
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<tt class='indentedcode'>| ------ | ----- |</tt>
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<tt class='indentedcode'>| 000 | 3 |</tt>
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<tt class='indentedcode'>| 001 | 10 |</tt>
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<tt class='indentedcode'>| 002 | 20 |</tt>
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<tt class='indentedcode'>| 003 | 30 |</tt>
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<br/><br/>
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You can construct one on the fly by keeping a pointer to
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<span class="tt">here</span> and using <span class="tt">,</span> to place the values. E.g.,
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<br/><br/>
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<tt class='indentedcode'>here [ #3 , #10 , #20 , #30 , ] dip</tt>
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<br/><br/>
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An example of this can be seen in this excerpt from an example
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(<strong>example/Primes.forth</strong>):
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<br/><br/>
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<tt class='indentedcode'>:create-set (-a) </tt>
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<tt class='indentedcode'> here #3000 , #2 #3002 [ dup , n:inc ] times drop ;</tt>
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</p>
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</body></html>
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