This gem uses embed V8 JavaScript engine and feelin JavaScript library to parse and evaluate DMN FEEL expressions. Performance of this approach for executing JS in Ruby is comparable with V8 native performance.

gem 'feelin'

# without context
FEELIN.evaluate('for a in [1, 2, 3] return a * 2') # [ 2, 4, 6 ]

# with context
FEELIN.evaluate("Mike's daughter.name", { 'Mike\'s daughter.name' => 'Lisa' }) # Lisa

# without context
FEELIN.unary_test('1', 1) # true

# with context
FEELIN.unary_test('[1..end]', 1, { 'end' => 10 }) # true

FEELIN.add_function('rates', proc { [10, 20] })
FEELIN.evaluate('every rate in rates() satisfies rate < 10') # false

The gem embeds the feelin JavaScript library, pre-bundled into a single file that is loaded into the V8 context at runtime. The JavaScript sources live in lib/feelin/js.

cd lib/feelin/js
npm install                  # install the pinned versions
npm install feelin@<version> # bump feelin to a specific version

feelin is distributed as an ES module, so it is bundled ahead of time with esbuild into lib/feelin/js/dist/feelin.js — an IIFE that exposes the feelin API on the global feel. The entry point is lib/feelin/js/entry.js.

cd lib/feelin/js
npm run build

Commit the regenerated dist/feelin.js together with the updated package.json / package-lock.json.

bundle exec rspec

Because this library is a wrapper - it is released with the same major/minor version numbers as the underlying feelin library