# Common Expression Language (Rust)
[](https://github.com/cel-rust/cel-rust/actions/workflows/rust.yml)
The [Common Expression Language (CEL)](https://github.com/google/cel-spec) 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.
```java
// Check whether a resource name starts with a group name.
resource.name.startsWith("/groups/" + auth.claims.group)
```
```go
// Determine whether the request is in the permitted time window.
request.time - resource.age < duration("24h")
```
```typescript
// Check whether all resource names in a list match a given filter.
auth.claims.email_verified && resources.all(r, r.startsWith(auth.claims.email))
```
## Getting Started
Add `cel` to your `Cargo.toml`:
```toml
[dependencies]
cel = "0.12.0"
```
Create and execute a simple CEL expression:
```rust
use cel::{Context, Program};
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());
}
```
### Examples
Check out these other examples to learn how to use this library:
- [Simple](./example/src/simple.rs) - A simple example of how to use the library.
- [Variables](./example/src/variables.rs) - Passing variables and using them in your program.
- [Functions](./example/src/functions.rs) - Defining and using custom functions in your program.
- [Concurrent Execution](./example/src/threads.rs) - Executing the same program concurrently.