expr4j

This project is a heavily tuned fork of the original expr4j/expr4j expression engine. The upstream repository went offline, so this fork keeps the project accessible while adding better packaging, docs, and ready-to-use shaded artifacts. It keeps the generic, token-based parser but streamlines module publishing for plugin ecosystems and JVM apps alike.

Modules & Packaging

All published artifacts live under the me.croabeast.expr4j group. The repository provides both regular and shaded JARs:

• Core - me.croabeast.expr4j:core: Required by every implementation.
• Double - me.croabeast.expr4j:double: Depends on core.
• Big Decimal - me.croabeast.expr4j:big-decimal: Depends on core and ch.obermuhlner:big-math:2.3.2.
• Complex - me.croabeast.expr4j:complex: Depends on core and org.apache.commons:commons-numbers-complex:1.2.
• Shaded variants - me.croabeast.expr4j:<module>-shaded: Bundle core and the module's own dependencies for drop-in use.

Big-decimal and complex implementations require their external libraries when using the non-shaded artifacts; you can declare them as dependencies or add them as libraries in your plugin.yml. The shaded artifacts already include everything, so you can reference them directly.

Non-shaded Dependency Examples

Add the repository and declare the dependencies you need. Non-shaded big-decimal and complex require their math libraries:

If you only need one implementation, keep core plus your chosen module. Shaded variants ( <module>-shaded) already bundle core and the external math libraries.

Repository

Artifacts are published to https://croabeast.github.io/repo/ with the path me/croabeast/expr4j. Add the repository and pick the modules you need.

Gradle (Kotlin DSL)

Maven

If you prefer shaded binaries, replace double or big-decimal / complex with <module>-shaded and omit the extra dependencies.

Quick Start

Create a builder for your numeric type, register variables, and evaluate:

Complex and BigDecimal builders expose the same API, so swapping types is effortless when you need more precision or imaginary components.

Implementation Notes

• Parsing relies on Dijkstra's shunting-yard algorithm to produce an AST and supports implicit multiplication, such as 2x or (a+b)(a-b).
• Operators and functions are lazy-evaluated, making it easy to plug in custom logic without recomputing unchanged branches.
• Builders are generic: extend Builder<T> with a custom Codec to support new numeric domains.

If you want to load non-shaded modules instead, add both core and the implementation, plus the external libraries in the same libraries block.

Why This Fork?

• Upstream hosting disappeared, so the fork keeps expr4j available with stable coordinates.
• Unified publishing for every module under a single repository path: me/croabeast/expr4j.
• Shaded variants tailored for plugin ecosystems.
• Expanded documentation, richer Javadoc, and examples that match the maintained repository.