Rhai is an embedded scripting language and evaluation engine for Rust that gives a safe and easy way to add scripting to any application.

Targets and builds

• All CPU and O/S targets supported by Rust, including:
  • WebAssembly (WASM)
  • no-std
• Minimum Rust version 1.57

Standard features

• Simple language similar to JavaScript+Rust with dynamic typing.
• Fairly efficient evaluation (1 million iterations in 0.3 sec on a single-core, 2.3 GHz Linux VM).
• Tight integration with native Rust functions and types, including getters/setters, methods and indexers.
• Freely pass Rust values into a script as variables/constants via an external Scope - all clonable Rust types are supported; no need to implement any special trait. Or tap directly into the variable resolution process.
• Built-in support for most common data types including booleans, integers, floating-point numbers (including Decimal), strings, Unicode characters, arrays (including packed byte arrays) and object maps.
• Easily call a script-defined function from Rust.
• Relatively little unsafe code (yes there are some for performance reasons).
• Few dependencies - currently only smallvec, num-traits, ahash, bitflags and smartstring.
• Re-entrant scripting engine can be made Send + Sync (via the sync feature).
• Compile once to AST form for repeated evaluations.
• Scripts are optimized (useful for template-based machine-generated scripts).
• Easy custom API development via plugins system powered by procedural macros.
• Function overloading and operator overloading.
• Dynamic dispatch via function pointers with additional support for currying.
• Closures (anonymous functions) that can capture shared values.
• Some syntactic support for object-oriented programming (OOP).
• Organize code base with dynamically-loadable modules, optionally overriding the resolution process.
• Serialization/deserialization support via serde (requires the serde feature).
• Support for minimal builds by excluding unneeded language features.
• A debugging interface.

Protected against attacks

• Don’t Panic guarantee - Any panic is a bug. Rhai subscribes to the motto that a library should never panic the host system, and is coded with this in mind.
• Sand-boxed - the scripting engine, if declared immutable, cannot mutate the containing environment unless explicitly permitted.
• Rugged - protected against malicious attacks (such as stack-overflow, over-sized data, and runaway scripts etc.) that may come from untrusted third-party user-land scripts.
• Track script evaluation progress and manually terminate a script run.
• Passes Miri.

For those who actually want their own language

• Use as a DSL.
• Disable certain language features such as looping.
• Further restrict the language by surgically disabling keywords and operators.
• Define custom operators.
• Extend the language with custom syntax.