Using Steel as an embedded scripting engine

Steel can be used as a scripting language within a Rust program. You can achieve this by creating a Steel Engine object. The Engine object allows you to execute Scheme code and interact with it from your Rust program. For more details about Engine, see the Engine API.

Steel Engine

The Steel Virtual Machine is provided by the steel-core trait.

[dependencies]
steel-core = { git="https://github.com/mattwparas/steel.git", branch = "master" }

The following example runs a few expressions in a Steel Engine and asserts that the results are as expected.

use steel::steel_vm::engine::Engine;
use steel::SteelVal;

fn main() {
    let mut steel_engine = Engine::new();
    let answer = steel_engine.run(
        "(+ 1 2 3 4)
         (+ 5 6 7 8)",
    );
    assert_eq!(answer, Ok(vec![SteelVal::IntV(10), SteelVal::IntV(26)]));
}

Engine::new

Creates a new engine. The Engine is used to run Steel Scheme code. Note that the Engine is not Send or Sync. This means it is bound to the current thread and cannot be shared or sent across other threads.

let mut steel_engine = Engine::new();

Engine::run

Runs a Steel expression and returns the result as a Result<Vec<SteelVal>>. If any error occurs, then Err(SteelErr) is returned.

let mut steel_engine = Engine::new();
assert_eq!(steel_engine.run("(+ 1 1)"), Ok(vec![SteelVal::IntV(2)]));
assert!(steel_engine.run("(+ 1 undefined-identifier)").is_err());

Embedding The Steel REPL

Repl functionality is provided by the steel-repl crate.

[dependencies]
steel-repl = { git="https://github.com/mattwparas/steel.git", branch = "master" }

run_repl

run_repl runs the Steel repl until an IO error is encountered or the user exits the repl. The repl may be exited by:

• Running the (quit) Steel Scheme function.
• Pressing either ctrl+c or ctrl+d within the repl.

let steel_engine = Engine::new();
steel_repl::run_repl(steel_engine).unwrap();