Getting Started

Overview

@veridtools/feel-parser is the lexer and parser for the FEEL expression language (Friendly Enough Expression Language), as defined in the OMG DMN 1.5 specification.

It converts a FEEL source string into a typed AST (AstNode) that can be evaluated, validated, introspected, or compiled into another representation.

FEEL string ──► tokenize() ──► Token[]
FEEL string ──► parse()    ──► AstNode

feel-runner

If you want to evaluate FEEL expressions against a context, see @veridtools/feel-runner. It uses this package internally.

Install

pnpm

pnpm add @veridtools/feel-parser

npm

npm install @veridtools/feel-parser

yarn

yarn add @veridtools/feel-parser

Quickstart

Parse an expression

import { parse } from '@veridtools/feel-parser';

const ast = parse('(1 + 2) * 3');
// { type: 'BinaryOp', op: '*', left: ..., right: ... }

Tokenize

import { tokenize } from '@veridtools/feel-parser';

const tokens = tokenize('1 + 2');
// [
//   { type: 'Number', value: '1', start: 0, end: 1 },
//   { type: 'Plus',   value: '+', start: 2, end: 3 },
//   { type: 'Number', value: '2', start: 4, end: 5 },
//   { type: 'EOF',    value: '',  start: 5, end: 5 },
// ]

Unary-test dialect

import { parse } from '@veridtools/feel-parser';

const ast = parse('"A","B","C"', 'unary-tests');
// { type: 'UnaryTestList', negated: false, tests: [...] }

Known names

import { parse } from '@veridtools/feel-parser';

const names = new Set(['Monthly Salary', 'Full Name']);
const ast = parse('Monthly Salary * 12', 'expression', names);
// Identifier { name: 'Monthly Salary' }  ← assembled as one node

Without knownNames, Monthly and Salary would each become separate identifiers.