Description

This is a parser for propositional logic; it will tell you whether a string is a well-formed formula of propositional logic.

Installation

Run:

npm i prop-parser --save

Input Formatting

Prop-Parser interprets uppercase characters (A-Z) as sentence letters and interprets a set of symbols as logical operators.

• ~ - Negation
• ^ - Conjunction
• v - Disjunction
• -> - Conditional
• <-> - Biconditional

A formula in propositional logic that is well formed can be defined recursively as follows:

1. Any single sentence letter (A-Z) is a WFF e.g. A
2. Any WFF prepended with a negation (~) is a WFF e.g. ~A
3. Any binary operator (^, v, ->, <->) inserted between two WFF surrounded by parentheses is a WFF e.g. (~A v B)
4. Nothing else is a WFF

It is important to call the wff_parse function on a single string of propositions followed by a newline (e.g. 'A ^ B\nA\n').

Usage

To load into your Node.js program, include the wff_parse function.

// import wff_parse function
const { wff_parse } = require('prop-parser');

// run function on a WFF
console.log(wff_parse("P -> Q\nP\nQ\n"));

// run function on a non-WFF
console.log(wff_parse("P -> ~\n"));

This will output:

1
0