86 lines
1.8 KiB
Text
86 lines
1.8 KiB
Text
# Quotations
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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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## Using Quotations
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To make a quotation, surround the code with square brackets. E.g.,
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#1 #2 eq? [ 'No_match s:put nl ] -if
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Quotes can be nested:
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[ #3 [ #4 ] dip ] call
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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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## Combinators
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Words operating on quotations are called combinators; these are
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discussed in *Using Combinators*.
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## Implementation
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A quotation is compiled as:
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... code before quotation ...
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i liju.... (if_compiling_only)
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d address after quotation (if_compiling_only)
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... code for quotation
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i re...... (this_is_where_the_quote_ends)
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i li......
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d address of code for quotation
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... code after quotation ....
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## Other Notes
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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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For instance, in a traditional Forth, you might have some
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conditionals:
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IF ... THEN
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IF ... ELSE ... THEN
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IF ... EXIT THEN
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RETRO uses conditional combinators for these:
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[ ... ] if
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[ ... ] [ ... ] choose
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[ ... ] if;
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Or loops:
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FOR ... NEXT
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Is replaced by:
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[ ... ] times
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This can also extend to stack flow. Sequences like:
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>R ... >R
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DUP >R ... >R
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Become:
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[ ... ] dip
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[ ... ] sip
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And forms like:
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1 2 3 * swap 3 * swap
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Can be replaced with a combinator like:
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#1 #2 [ #3 * ] bi@
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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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