The Common Expression Language (CEL) is a non-Turing complete language designed for simplicity, speed, safety, and portability. CEL's C-like syntax looks nearly identical to equivalent expressions in C++, Go, Java, and TypeScript. CEL is ideal for lightweight expression evaluation when a fully sandboxed scripting language is too resource intensive.

// Check whether a resource name starts with a group name.
resource.name.startsWith("/groups/" + auth.claims.group)

// Determine whether the request is in the permitted time window.
request.time - resource.age < duration("24h")

// Check whether all resource names in a list match a given filter.
auth.claims.email_verified && resources.all(r, r.startsWith(auth.claims.email))

This project includes a CEL-parser and an interpreter which means that it can be used to evaluate CEL-expressions. The library aims to be very simple to use, while still being fast, safe, and customizable.

fn main() {
    let program = Program::compile("add(2, 3) == 5").unwrap();
    let mut context = Context::default();
    context.add_function("add", |a: i64, b: i64| a + b);
    let value = program.execute(&context).unwrap();
    assert_eq!(value, true.into());
}

Check out these other examples to learn how to use this library:

• Simple - A simple example of how to use the library.
• Variables - Passing variables and using them in your program.
• Functions - Defining and using custom functions in your program.
• Concurrent Execution - Executing the same program concurrently.