Logical Expressions Core Module

Description

A TypeScript module that parses, transforms, derives and evaluates logic expressions. Can be easily extended to support more operators, variables, notations, etc.

Quick Examples

(Test more examples using the demo, see demo/README.md)

Transform a'(ab'+c)' to it's expanded DNF using boolean algebra:

Installation

• install from repository:

git clone https://github.com/larsfrs/logic-expr-core.git
cd logic-expr-core
npm install
npm run build

• then you can use it in your project by either:

  • creating a symlink with npm link (good for development)
  • importing it directly from the dist folder (or copy the contents of the dist folder to your project)

• install with npm:

npm install logic-expr-core

Features

• parse string of expression to RPN (Reverse Polish Notation)

  • a*!(b|c) => a b c | ! *
  • handle different notations like postfix and prefix, add/omit "and" operators, etc.

• parse RPN to a binary AST (Abstract Syntax Tree)

  BinaryOperatorNode (AND)
  ├── LeafNode (a)
  ├── UnaryOperatorNode (NOT)
  │   └── BinaryOperatorNode (OR)
  │       ├── LeafNode (b)
  │       └── LeafNode (c)
  

• evaluate binary AST to boolean value

  const result: boolean = evaluateExpression("a!(b+c)", { a: true, b: false, c: true }, booleanContext);
  console.log(result); // false

• turn binary AST to n-ary AST (more than 2 children per node)

  BinaryOperatorNode (AND)
  ├── LeafNode (a)
  ├── BinaryOperatorNode (AND)
  │   ├── LeafNode (b)
  │   └── LeafNode (c)
  

  • turns into n-ary AST: (and back)

  NaryOperatorNode (AND)
  ├── LeafNode (a)
  ├── LeafNode (b)
  └── LeafNode (c)
  

• apply transformative laws to the AST

  • e.g. distributive law, absorption law, de Morgan's law, etc.

• transform the AST to different normal forms (NNF, DNF)

  • show every step of the transformation and output a list of transformations

• visualization of the expression tree and transformations

In development

• equivalence checking (using truth tables, CNF and DNF, etc.)

Goal

• create a module for visualizing transformations of expressions in boolean algebra
• show through the code how to implement a parser, AST, evaluator, etc. in TypeScript
• make it easy to extend and customize for different use cases
• keep it small and simple, without unnecessary dependencies

Keywords

logic, boolean algebra, expressions, parser, AST, abstract syntax tree, RPN, reverse polish notation, evaluator, normal forms, DNF, CNF, NNF, TypeScript