ksl 0.1.30

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

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

pub(crate) fn builtin(args: &[Value], env: Environment) -> Result<Value, std::sync::Arc<str>> {
    if let [obj, key, val] = args {
        match (eval_apply(obj, env.clone())?, eval_apply(key, env.clone())?) {
            (Value::Object(type_name, mut dict), Value::Atom(k)) => {
                let _ = dict.insert(k, std::sync::Arc::new(eval_apply(val, env)?));
                Ok(Value::Object(type_name, dict))
            }
            (Value::List(lst), Value::Number(idx)) if (idx as usize) > lst.len() => Err(std::sync::Arc::from(format!(
                concat!(
                    "Error[ksl::builtin::Index]: ",
                    "Index `{}` out of bounds `{}`."
                ),
                idx.trunc(),
                lst.len()
            ))),
            (Value::List(lst), Value::Number(idx)) if is_number_eq(idx, idx.trunc()) && idx > 0.0 => {
                let mut new_vec = lst.to_vec();
                new_vec[(idx as usize) - 1] = eval_apply(val, env)?;
                Ok(Value::List(std::sync::Arc::from(new_vec)))
            }
            (Value::List(lst), Value::Number(idx)) if is_number_eq(idx, -1.0) => {
                let len = lst.len();
                let mut new_vec = lst.to_vec();
                new_vec[len - 1] = eval_apply(val, env)?;
                Ok(Value::List(std::sync::Arc::from(new_vec)))
            }
            (Value::List(_), Value::Number(idx)) => Err(std::sync::Arc::from(format!(
                concat!(
                    "Error[ksl::builtin::Set]: ",
                    "Expected an integer greater than 0, but got {}."
                ),
                idx
            ))),
            (Value::Object(_, _) | Value::List(_), e) => Err(std::sync::Arc::from(format!(
                concat!("Error[ksl::builtin::Set]: ", "Unexpected value: `{}`."),
                e
            ))),
            (e, _) => Err(std::sync::Arc::from(format!(
                concat!("Error[ksl::builtin::Set]: ", "Unexpected value: `{}`."),
                e
            ))),
        }
    } else {
        Err(std::sync::Arc::from(format!(
            concat!(
                "Error[ksl::builtin::Set]: ",
                "Expected 3 parameters, but {} were passed."
            ),
            args.len()
        )))
    }
}