ksl 0.1.7

KSL core library and interpreter
Documentation 
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//! # ksl::builtin::set
//!
//! Built-in function `Set`.

use crate::{Environment, eval::apply::eval_apply, value::Value};

pub(crate) fn builtin(args: &[Value], env: &Environment) -> Option<(Value, Environment)> {
    if let [obj, key, val] = &args[..] {
        match (
            eval_apply(obj, env),
            eval_apply(key, env),
            eval_apply(val, env),
        ) {
            (Some((Value::Object(type_name, mut dict), _)), Some((Value::String(k), _)), Some((e, new_env))) => {
                let _ = dict.insert(k, e);
                Some((Value::Object(type_name, dict), new_env))
            }
            (Some((e1, _)), Some((e2, _)), Some((e3, _))) => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::set]: ",
                        "Only accepts an object, a string of key and a value as arguments, ",
                        "but {:?} were passed."
                    ),
                    (e1, e2, e3)
                );
                None
            }
            _ => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::set]: ",
                        "Cannot evaluate expression {:?}."
                    ),
                    (obj, key, val)
                );
                None
            }
        }
    } else {
        eprintln!(
            concat!(
                "Error[ksl::builtin::set]: ",
                "Only accepts 3 arguments, but {} were passed."
            ),
            args.len()
        );
        None
    }
}