88 lines
5.1 KiB
HTML
88 lines
5.1 KiB
HTML
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<title>doc/book/techniques/stack-diagrams</title>
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<p><span class="h1">Stack Diagrams</span>
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<br/><br/>
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Most words in RETRO have a stack comment. These look like:
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<br/><br/>
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<tt class='indentedcode'>(-)</tt>
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<tt class='indentedcode'>(nn-n)</tt>
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<br/><br/>
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As with all comments, a stack comment begins with <span class="tt">(</span> and
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should end with a <span class="tt">)</span>. There are two parts to the comment.
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On the left side of the <span class="tt">-</span> is what the word <strong>consumes</strong>. On
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the right is what it <strong>leaves</strong>.
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<br/><br/>
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RETRO uses a short notation, with one character per value
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taken or left. In general, the following symbols represent
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certain types of values.
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<br/><br/>
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<tt class='indentedcode'>| Notation | Represents |</tt>
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<tt class='indentedcode'>| ------------------- | ----------------------- |</tt>
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<tt class='indentedcode'>| b, n, m, o, x, y, z | generic numeric values |</tt>
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<tt class='indentedcode'>| s | string |</tt>
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<tt class='indentedcode'>| v | variable |</tt>
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<tt class='indentedcode'>| p, a | pointers |</tt>
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<tt class='indentedcode'>| q | quotation |</tt>
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<tt class='indentedcode'>| d | dictionary header |</tt>
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<tt class='indentedcode'>| f | `TRUE` or `FALSE` flag. |</tt>
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<br/><br/>
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In the case of something like <span class="tt">(xyz-m)</span>, RETRO expects z to be
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on the top of the stack, with y below it and x below the y
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value. And after execution, a single value (m) will be left on
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the stack.
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<br/><br/>
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Words with no stack effect have a comment of (-)
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<br/><br/>
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For combinators (words consuming quotations), you can include
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a sub-comment indicating the expected stack effect of the
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quote. E.g.,
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<br/><br/>
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<tt class='indentedcode'>(q(-f)-)</tt>
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<br/><br/>
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Indicates a word consuming a quote and returning nothing. The
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quote should return a flag.
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</p>
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</body></html>
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