Function fold

src/selector.rs:239–252

(helper: &MyHelper, init: Exp, vs: Vec<IDLValue>, func: &str)

}

fn fold(helper: &MyHelper, init: Exp, vs: Vec<IDLValue>, func: &str) -> Result<IDLValue> {
    let init = init.eval(helper)?;
    let mut new_helper = helper.spawn();
    let mut acc = init;
    for v in vs.into_iter() {
        new_helper.env.0.insert(String::new(), v);
        let arg = Exp::Path(String::new(), Vec::new());
        new_helper.env.0.insert("_".to_string(), acc.clone());
        let accu = Exp::Path("_".to_string(), Vec::new());
        let exp = Exp::Apply(func.to_string(), vec![accu, arg]);
        acc = exp.eval(&new_helper)?;
    }
    Ok(acc)
}