rmutt.js is a tool for generating random text from context-sensitive grammars. It's a reimplementation of the C project rmutt by Joe Futrelle, which in turn is modeled after Andrew C. Bulhak's late, great Dada Engine which he used to write the hilarious Postmodernism Generator. rmutt.js grammar is backward compatible with the original rmutt, but adds features inspired by Dada Engine such as indirection and JavaScript platform capabilities, like embedded code and external rules.
The original rmutt was named after Marcel Duchamp's alter-ego Richard Mutt, who is responsible for the "urinal" ready-made, an infamous dadaist art prank. rmutt is not to be confused with the UNIX mail-reader mutt.
rmutt takes as input a set of user-supplied grammatical rules, each of which represents a set of choices that can be made at a particular level of grammatical description. For instance a grammar might specify that a "person" can be either "Fred" or "Jennifer". rmutt then makes these choices randomly, resulting in text which conforms to the grammar but is otherwise unpredictable.
Grammars in rmutt need not relate in any way to the grammar of any human language. For instance, rmutt can be used to generate text instructions for producing graphics or music.
rmutt is similar to the Dada Engine, in that its grammars can be made context-sensitive by means of variable assignment and/or grammar self-modification. For instance a choice made in one rule may affect the definition of another rule. Also, textual transformations can be applied to the output of rules using regular expressions, by which means a rule can modify the output of more than one other rule. This is a bit like Chomsky's notion of a transformational grammar.
Here's a simple rmutt grammar. For an explanation of the syntax, see the user's guide.
s: np " " vp ".";
np: art " " noun, propn;
art: "the", "a";
noun: "cat", "dog";
propn: "Joe", "Beth";
vp: iv, tvp;
iv: "meowed", "barked";
tvp: tv " " np;
tv: "scolded", "loved";Each rule has a name and is defined as a set of choices, separated by commas. Each choice is defined as a sequence of either the name of a rule to invoke at that point in the grammar, or a literal string to print out. In the first rule, s is defined as an np followed by a space followed by a vp followed by a period. In the second rule, np is defined as either an art followed by a space followed by a noun; or a propn. And so on.
Here are some sample strings rmutt produced with this grammar:
Joe barked.
a cat scolded the dog.
Joe loved the dog.
Beth scolded Beth.
Beth meowed.
Joe loved a dog.
a dog barked.
You can see that the output at each point depends on which rules have been invoked as rmutt traverses the hierarchy of choices. Now let's add something simple to demonstrate that the rules need not have a strict hierarchical relationship to one another. In this example we add a tvp which includes an s:
s: np " " vp ".";
np: art " " noun, propn;
art: "the", "a";
noun: "cat", "dog";
propn: "Joe", "Beth";
vp: iv, tvp;
iv: "meowed", "barked";
tvp: tv " " np , "said that " s;
tv: "scolded", "loved";This kind of circularity is perfectly legal in rmutt. Here are some example strings produced by this grammar:
Joe scolded Beth.
Beth said that Joe meowed..
a cat barked.
a dog said that a cat meowed.
Beth said that a cat said that Joe said that the dog meowed....
Notice that in the last example string, the top-level s contained an s which contained its own s which itself contained an s. This is allowable according to the grammar, since any s may contain another s. In fact, rmutt would run forever like this if there were no choices available to it that did not contain the embedded s. Do you see a problem with the grammar? There are multiple periods after the examples with "said that" in them. This is because there's a period in the definition of s, so any string containing more than one s will have multiple periods in it. That can be fixed in the following manner:
top: s ".";
s: np " " vp;
np: art " " noun, propn;
art: "the", "a";
noun: "cat", "dog";
propn: "Joe", "Beth";
vp: iv, tvp;
iv: "meowed", "barked";
tvp: tv " " np, "said that " s;
tv: "scolded", "loved";This simple example is just a hint of what rmutt can do. For more information see:
- The user's guide.
- The command-line interface documentation.
- The JavaScript API documentation.
- Find inspiration in the example grammars.
This overview is mostly based on the original rmutt documentation by Joe Futrelle.