--- /dev/null
+ GNU GENERAL PUBLIC LICENSE
+ Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
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+
+ Preamble
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+ GNU GENERAL PUBLIC LICENSE
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+
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+ NO WARRANTY
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+ END OF TERMS AND CONDITIONS
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+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
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+ To do so, attach the following notices to the program. It is safest
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+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
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+ This program is free software; you can redistribute it and/or modify
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+
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+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
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+
+ Gnomovision version 69, Copyright (C) year name of author
+ Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary. Here is a sample; alter the names:
+
+ Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+ `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+ <signature of Ty Coon>, 1 April 1989
+ Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs. If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
--- /dev/null
+# Recursive Random Rewrites
+
+RRR is a JavaScript library which repeatedly applies replacements to a
+string. This can be used to generate a wide variety of random text. It
+is sort of like, but is not, an [L-system][], a [Markov machine][], or
+a [stochastic grammar][].
+
+RRR works by specifying a grammar using [BNF][]-like rules (easily
+specified with JSON). An object providing the production rules,
+mapping the names to possible expansions, is provided to the `Grammar`
+constructor. Possible productions are specified as an object mapping a
+production to a numeric weight.
+
+The `Grammar`'s `expand` method then randomly expands an input string
+based on the grammar specified.
+
+For convenience, possible productions may also be provided as a list
+or string, in which case each item has equal weight. RRR also provides
+some syntactic sugar for repetition:
+
+* `<A>{n}` - Repeat rule `A` `n` times.
+* `<A>{n,m}` - Repeat rule `A` a random number of times between `n`
+ and `m` (uniformly, inclusive).
+* `<A>?` - Produce rule `A` ½ of the time, and nothing ½ of the time.
+* `<A>*` - Produce nothing ½ of the time, `<A>` ¼ of the time,
+ `<A><A>` ⅛ of the time, and so on.
+* `<A>+` - Produce `<A>` ½ of the time, `<A><A>` ¼ of the time,
+ `<A><A><A>` ⅛ of the time, and so on.
+
+Repetition patterns can also be specified with a space after the rule
+name, e.g. `<A >+`. In this case, the repetitions have spaces between
+them, e.g. `<A> <A>`.
+
+Production rules are case-sensitive. By convention, terminals start
+with a lowercase letter.
+
+## Example
+
+The following is the term/expression/factor grammar you might
+encounter in a textbook about parsing. However, instead
+of _parsing_ equations, RRR will generate random ones.
+
+(This example is also available as a loadable module in the included
+`term.js` file.)
+
+ ::javascript
+ var grammar = new rrr.Grammar({
+ // Canonical expression/term/factor grammar.
+
+ Expr: ['<Term>', '<Term> + <Term>', '<Term> - <Term>'],
+ Term: ['<Fact>', '<Fact> * <Fact>', '<Fact> / <Fact>'],
+ Sign: ['-', ''],
+
+ // If a parenthesized expression is as likely as a number, the
+ // expansion explodes and overflows the stack. You can prove
+ // this by multiplying out the probabilities: On average, Expr
+ // produces 5/3 Terms, Terms produce 5/3 Facts, and Fact
+ // produces 1/2 Exprs.
+ //
+ // So with equal weights Expr produces, on average,
+ // (5/3)*(5/3)*(1/2) ~= 1.4 Exprs.
+ //
+ // That means Expr must be weighed at _most_ 1/1.4 ~= 0.72
+ // relative to the other option to produce one Expr, and in
+ // practice should be even less to avoid "lucky" stack
+ // overflows.
+ Fact: { '<Number>': 1, '<Sign>(<Expr>)': 0.4 },
+
+ // A numeral may not begin with a 0.
+ Number: ['<Sign><digit><digit0>*'],
+ digit: '123456789',
+ digit0: '1234567890'
+
+ }, '<Expr>'); // This is the default start token.
+
+To generate a random equation, call `grammar.generate()`. If you want
+a start expression other than the default, you can provide a different
+initial string.
+
+ ::javascript
+ grammar.generate(); // Equivalent to grammar.generate('<Expr>')
+ // => '-9 * 3512 + (-(-51 - -9 / 6) / -6278 + -4 * 30321) / 21940'
+
+ grammar.generate('Solve: <Expr>');
+ // => 'Solve: 7 + (255 * (4 / 18))'
+
+ grammar.generate("Today's numbers are <Number> and <Number>.");
+ // => 'Today\'s numbers are 94 and -142.'
+
+Because RRR is not parsing and unconcerned with ambiguity, some of the
+standard rules could be simplified. For example, `Expr` could be
+written as `<Fact> <op> <Fact>` (with `op` defined as `+-*/`),
+removing the need for `Term`. Such a grammar would still generate only
+valid expressions, but with slightly different probabilities.
+
+## FAQ
+
+### Why doesn't `expand` return?
+### Why do I get `RangeError: Maximum call stack size exceeded`?
+
+Your grammar contains infinitely recursive rules. This is not
+currently handled.
+
+### Why aren't `foo{4}`, `foo+`, etc. working?
+
+Repetition modifiers only apply to rules, not literals.
+
+### Can I use `+` but with a chance other than ½?
+
+If you need probabilities other than 50% you can use weighted rules, e.g.
+
+ { A: { '<foo>": 0.8, "<foo><A>": 0.2 } }
+
+will contain one `<foo>` 80% of the time, two 16% of the time, three
+3.2% of the time, etc.
+
+
+[L-system]: http://en.wikipedia.org/wiki/L-system
+[Markov machine]: http://en.wikipedia.org/wiki/Markov_algorithm
+[stochastic grammar]: http://en.wikipedia.org/wiki/Stochastic_grammar
+[BNF]: http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form
projects / rrr.git / commitdiff