Tweakflow: Expression Evaluation for JVM Apps
I needed to evaluate Excel-like expressions inside a Kotlin/JVM application — user-defined formulas, not hardcoded logic. After evaluating options, I found Tweakflow and it hit every requirement.
What it is
Tweakflow is an embeddable expression language for the JVM. Users write expressions; your app evaluates them. No full scripting engine, no security nightmares.
Why it works
Simple model. Only values and functions. No classes, no paradigms to learn. Application users
can write date + 7d without understanding programming.
Dynamically typed. Supports booleans, strings, longs, doubles, decimals, datetimes, functions, lists, and dicts — all with literal notation.
Immutable data. All values are immutable. Safe to pass between user expressions and host app without worrying about shared state.
Pure functions. No side effects. Given the same inputs, always the same output. Makes caching and testing trivial.
Sandboxed. The host application controls exactly what the expression environment can access. Users cannot reach into your JVM state.
Embeddable. Ships as a JAR. No native deps, no daemon process.