@bpmnkit/feel

FEEL (Friendly Enough Expression Language) parser, evaluator, formatter and highlighter — 94% DMN TCK conformance

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Core tier. Semver at 1.0: nothing breaks without a major release. See product tiers.

Overview

@bpmnkit/feel implements the FEEL expression language used in DMN decision tables and BPMN condition expressions, and passes 1,941 of the 2,053 FEEL cases in the DMN TCK (94.5%) — the remaining cases are listed with their reasons in tests/tck.test.ts. It implements Camunda 8's extensions to FEEL too, and matches 375 of the 378 runnable examples in Camunda's FEEL documentation (tests/camunda-parity.test.ts). It includes a tokenizer, recursive-descent parser, AST evaluator, formatter, and syntax highlighter.

Features

• Full FEEL grammar — arithmetic, comparisons, logic, function calls, paths, filters
• Temporal types — date, time, datetime, duration (ISO 8601, full spec compliance)
• Unary tests — DMN input expression syntax (> 5, "gold", "silver", [1..10])
• Built-in functions — 101 FEEL functions (string, list, numeric, date, context, range), including Camunda's extensions (assert, partition, to json, fromAi, …)
• Range expressions — [1..10], (0..1), [today..end]
• Context literals — { key: value, nested: { x: 1 } }
• Syntax highlighting — semantic token classification for editors
• Zero dependencies

Installation

npm install @bpmnkit/feel

Quick Start

Evaluate an expression

import { parseExpression, evaluate } from "@bpmnkit/feel"

const parsed = parseExpression("amount * 1.2 + fee")
if (!parsed.errors.length) {
  // `evaluate` takes an EvalContext — variables live under `vars`.
  const result = evaluate(parsed.ast!, { vars: { amount: 100, fee: 5 } })
  console.log(result) // 125
}

Evaluate unary tests (DMN input expressions)

import { parseUnaryTests, evaluateUnaryTests } from "@bpmnkit/feel"

// Does input value match any listed condition?
const parsed = parseUnaryTests('"gold","silver"')
const matches = evaluateUnaryTests(parsed.ast!, "gold", { vars: {} })
console.log(matches) // true

Syntax highlighting

import { annotate, highlightToHtml } from "@bpmnkit/feel"

// Classified tokens, for an editor to style itself.
annotate("x > 1")[0] // { kind: "variable", value: "x", start: 0, end: 1 }

// Or the same tokens already wrapped in <span class="feel-…"> elements.
highlightToHtml('if x > 10 then "high" else "low"')

API Reference

ParseResult

interface ParseResult {
  ast: FeelNode | null
  errors: ParseError[]   // { message, start, end }
}

Related Packages

License

MIT © BPMN Kit — made by u11g