Added examples on how to use the library

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["cli", "parser", "interpreter"]
+members = ["cli", "parser", "interpreter", "example"]
 
 [profile.bench]
 lto = true

README.md

@@ -34,3 +34,11 @@ fn main() {
     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.

example/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "example"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+cel-interpreter = { path = "../interpreter" }
+
+[[bin]]
+name = "simple"
+path = "src/simple.rs"
+
+[[bin]]
+name = "variables"
+path = "src/variables.rs"
+
+[[bin]]
+name = "functions"
+path = "src/functions.rs"

example/src/functions.rs

@@ -0,0 +1,19 @@
+use cel_interpreter::{CelType, Context, Expression, Program, ResolveResult};
+
+fn main() {
+    let program = Program::compile("add(2, 3)").unwrap();
+    let mut context = Context::default();
+    context.add_function("add", add);
+
+    let value = program.execute(&context).unwrap();
+    assert_eq!(value, 5.into());
+}
+
+/// The add function takes two arguments and returns their sum. We discard the first
+/// parameter because the add function is not a method, it is always called with two
+/// arguments.
+fn add(_: Option<&CelType>, args: &[Expression], ctx: &Context) -> ResolveResult {
+    let a = CelType::resolve(args.get(0).unwrap(), ctx)?;
+    let b = CelType::resolve(args.get(1).unwrap(), ctx)?;
+    Ok(a + b)
+}

example/src/simple.rs

@@ -0,0 +1,8 @@
+use cel_interpreter::{Context, Program};
+
+fn main() {
+    let program = Program::compile("1 == 1").unwrap();
+    let context = Context::default();
+    let value = program.execute(&context).unwrap();
+    assert_eq!(value, true.into());
+}

example/src/variables.rs

@@ -0,0 +1,10 @@
+use cel_interpreter::{Context, Program};
+
+fn main() {
+    let program = Program::compile("foo * 2").unwrap();
+    let mut context = Context::default();
+    context.add_variable("foo", 10);
+
+    let value = program.execute(&context).unwrap();
+    assert_eq!(value, 20.into());
+}

interpreter/src/lib.rs

@@ -1,14 +1,14 @@
 extern crate core;
 
-use crate::context::Context;
-use crate::objects::{CelType, ResolveResult};
-use cel_parser::ast::Expression;
 use cel_parser::parser::ExpressionParser;
 use std::convert::TryFrom;
 use std::rc::Rc;
 use thiserror::Error;
 
 pub mod context;
+pub use cel_parser::Expression;
+pub use context::Context;
+pub use objects::{CelType, ResolveResult};
 mod duration;
 mod functions;
 pub mod objects;