logica

a compile-to-javascript predicate logic language

npm install logica
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logica

a compile-to-javascript predicate logic language

note: this is a preview public release, so documentation is a bit sparse right now.

logica is a language for expressing Boolean algebra. It's clean syntax makes it easy for non-programmers and domain experts to express complex logic and conditional knowledge.

  • flexible syntax
  • interpreted or compile-to-javascript
  • all operators support multiple arguments (except not)
  • extensible with custom predicate operators

basic usage

in logica, you create predicates (functions which result in a true or false value). The simplest predicate is a literal boolean value. That is, the following is valid logica:

true

This, clearly, will always evaluate to true. Of course, you probably want more complex things:

(OR
  (Today = "wednesday")
  (Today = "mittwoch")
)

Whitespace doesn't matter, but it can improve usability. Optionally, commas can be used to separate the various pieces. We could also write:

(OR,(Today="wednesday"),(=,Today,"mittwoch"))

Here, we're using a symbolic variable, Today, and comparing it to the literal values wednesday and mittwoch.

In JavaScript, you might write:

Today === "wednesday" || Today === "mittwoch"

Notice the parentheses? You can nest predicates as deeply as you'd like.

Note that since this predicate references Today, we can't evaluate it without a value for Today. It might help to think about it like this: in logica, you're writing a function. Each symbolic variable you use requires a corresponding argument. When using logica in JavaScript, these are supplied as properties on a state object which is passed in.

Putting it all together,

var logica = require('logica')

var source = '(OR (Today = "wednesday"), (Today = "mittwoch"))'

logica.exec(source, {Today: 'mittwoch'})
// => true

logica.exec(source, {Today: 'wednesday'})
// => true

logica.exec(source, {Today: 'tuesday'})
// => false

Now that you've got the basics, check out the /examples/ folder for more.

A slightly more elaborate (and contrived, but valid) predicate might be:

# a logica program

(AND
  (foo = 'baz')
  faa
  (NOT (NOT true))

  (pizzas >= 23)
  ('cheese' IN toppings)
  (and (foo = bar))
)

using the compiler

logica can be compiled to JavaScript sourcecode so that the overhead of parsing only has to occur once. For example, a server can pre-compile logica predicates for use on a client application.

in node, simply:

var compile = require('logica')

var jsCode = compile(sourceString, options);

using a compiled function

The compiler generates JavaScript sourcecode as a string. This intermediate form expects certain functions to exist in the runtime environment implementing logica operators.

The easiest way to consume this source is using the hydrate function:

var hydrate = require('logica/hydrate')
var logicaFn hydrate(compiledLogicaSource)

var state = { foo: true, bar: false }

var result = logicaFn(state)

Hydrate is a standalone module with no dependencies. You can use it, for example, to execute functions clientside that were precompiled on the server.

compile options

You can supply and opts object as the optional second argument of compile.

  • prettyPrint: boolean (default false). If true, will generate code with line breaks and indentation

examples

See the /examples folder. Files ending in .logica are plain logica source files.

running the unit tests

$ make test

hacking on the parser

logica's parser is implemented in jison. The lexer and parser definitions are implemented in the file logica.jison, which generates parser.js. This file will get overwritten - do not make modifications to this file. Instead, modifications can be made in logica.jison itself or in postParser.js, which is just JavaScript.

To generate parser.js:

$ make

contributors

Jason Denizac - jden - jason@denizac.org

license

MIT (c) 2013 Agile Diagnosis, Inc. See LICENSE.md

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