egg
is a toy Programming Language from the book Eloquent Javascript by Marijn Haverbeke, Chapter 12. The Book was pivotal to my early Programming journey. I moved to Rust some time back and in a fit of nostalgia I decided to rewrite egg
in Rust.
- Extensive and Modular standard library;
Core
,Objects
,StringTools
,Console
andFunctions
- Effective Scope Chain: Local Variables and Global Variables work as expected.
- User-Defined Functions: Create functions in Egg using the
fn
keyword. - Higher Order Functions: Pass functions as values to other functions or to built-in
Operators
. - Extensible: Create your own builtin functions by implementing the
Operator
trait. - no_std: Only depends on
alloc
. Enabling thestd
feature adds thePrint
,PrintLine
,ReadLine
andSleep
builtins.
To start executing a script, we need to first parse
it, create a Scope
and assemble a map of builtin functions it can access:
use egglang::prelude::*;
// Create the default Scope, with necessary constants set
let mut scope = Scope::default();
// Create a minimal set of operators
let mut operators = operators::empty();
operators::minimal(&mut operators);
// Parse a Script into a list of expressions
let script = "sum(12.5, 12.5, 25)";
let expressions = parse(script).unwrap();
// Evaluate the expression
let expression = &expressions[0]; // the call to `sum`
let result = evaluate(expression, &mut scope, &operators).unwrap();
assert_eq!(result, 50f32.into());
use egglang::prelude::*;
use std::collections::BTreeMap;
// Create the default Scope, with necessary constants set
let mut scope = Scope::default();
// Insert base operators, and add console functions; Adds println
let mut operators = operators::empty();
operators::minimal(&mut operators);
operators::console(&mut operators);
// Define a `random(...)` builtin
struct Random;
impl Operator for Random {
fn evaluate(&self, _: &[Expression], _: &mut Scope, _: &BTreeMap<&str, Box<dyn Operator>>) -> EggResult<Value> {
// totally random value ;)
Ok(0.15.into())
}
}
// Insert `random(...)` into Operators map
operators.insert("random", Box::new(Random));
// Parse a Script into a list of expressions
let script = r#"
define(iterations, random(0, 120))
repeat(iterations, println("oi oi oi oi oi"))
"#;
let expressions = parse(script).unwrap();
// Evaluate the expressions; define -> repeat -> ...
for expression in expressions {
let _ = evaluate(&expression, &mut scope, &operators).unwrap();
}
Example Egg scripts can be found in the
scripts
directory;