Function eval 

pub fn eval(expr: &Expr, env: &Env, fuel: Fuel) -> Result<(Value, Fuel), Error>

Evaluate expr against env with the given step budget.

Returns the resulting Value paired with the remaining fuel. The returned fuel can be threaded into further evaluations.

Errors

Returns Error::UnboundVariable if evaluation references a free variable not bound in env, or Error::FuelExhausted if reduction exceeds the budget.

Examples

use lambda_cat::env::Env;
use lambda_cat::eval::{eval, Fuel};
use lambda_cat::syntax::Expr;

let id = Expr::lam("x", Expr::var("x"));
let (value, _fuel) = eval(&id, &Env::empty(), Fuel::new(100))?;
assert_eq!(format!("{value}"), "\\x. x");