2021-01-21 13:40:28 +01:00
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2024-09-06 12:39:30 +02:00
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<title>doc/book/techniques/quotes</title>
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2021-01-21 13:40:28 +01:00
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</head><body>
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<p><span class="h1">Quotations</span>
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<br/><br/>
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Quotes are anonymous functions. RETRO uses these as the basis for
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executable flow control and combinatorial logic.
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<br/><br/>
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2024-09-06 12:39:30 +02:00
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<span class="h2">Using Quotations</span>
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<br/><br/>
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To make a quotation, surround the code with square brackets. E.g.,
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<br/><br/>
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<tt class='indentedcode'>#1 #2 eq? [ 'No_match s:put nl ] -if</tt>
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<br/><br/>
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Quotes can be nested:
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<br/><br/>
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<tt class='indentedcode'>[ #3 [ #4 ] dip ] call</tt>
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<br/><br/>
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After creation, a pointer to the quotation is left on the stack
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(or is compiled into the current definition).
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<br/><br/>
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<span class="h2">Combinators</span>
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<br/><br/>
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Words operating on quotations are called combinators; these are
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discussed in <strong>Using Combinators</strong>.
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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 quotation is compiled as:
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<br/><br/>
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<tt class='indentedcode'>... code before quotation ...</tt>
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<tt class='indentedcode'>i liju.... (if_compiling_only)</tt>
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<tt class='indentedcode'>d address after quotation (if_compiling_only)</tt>
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<tt class='indentedcode'>... code for quotation</tt>
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<tt class='indentedcode'>i re...... (this_is_where_the_quote_ends)</tt>
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<tt class='indentedcode'>i li......</tt>
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<tt class='indentedcode'>d address of code for quotation</tt>
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<tt class='indentedcode'>... code after quotation ....</tt>
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<br/><br/>
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<span class="h2">Other Notes</span>
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<br/><br/>
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Quotations are used heavily in RETRO. They give the source a
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feel that's different from traditional Forth, and allow for
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a more consistent syntax.
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<br/><br/>
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For instance, in a traditional Forth, you might have some
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conditionals:
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<br/><br/>
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<tt class='indentedcode'>IF ... THEN</tt>
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<tt class='indentedcode'>IF ... ELSE ... THEN</tt>
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<tt class='indentedcode'>IF ... EXIT THEN</tt>
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<br/><br/>
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RETRO uses conditional combinators for these:
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<br/><br/>
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<tt class='indentedcode'>[ ... ] if</tt>
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<tt class='indentedcode'>[ ... ] [ ... ] choose</tt>
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<tt class='indentedcode'>[ ... ] if;</tt>
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<br/><br/>
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Or loops:
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<br/><br/>
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<tt class='indentedcode'>FOR ... NEXT</tt>
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<br/><br/>
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Is replaced by:
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<br/><br/>
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<tt class='indentedcode'>[ ... ] times</tt>
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<br/><br/>
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This can also extend to stack flow. Sequences like:
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<br/><br/>
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<tt class='indentedcode'>>R ... >R</tt>
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<tt class='indentedcode'>DUP >R ... >R</tt>
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<br/><br/>
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Become:
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<br/><br/>
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<tt class='indentedcode'>[ ... ] dip</tt>
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<tt class='indentedcode'>[ ... ] sip</tt>
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<br/><br/>
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And forms like:
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<br/><br/>
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<tt class='indentedcode'>1 2 3 * swap 3 * swap</tt>
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<br/><br/>
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Can be replaced with a combinator like:
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<br/><br/>
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<tt class='indentedcode'>#1 #2 [ #3 * ] bi@</tt>
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<br/><br/>
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While there is a different set of words to learn, I find that
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overall there's less noise from low level stack shuffling words
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and the added consistency with regards to overall syntax has
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been nice as I was never fond of the multiple forms that existed
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in traditional Forth.
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</p>
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</body></html>
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