ksl 0.1.5

KSL core library and interpreter
Documentation 
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use crate::{Environment, eval::apply::eval_apply, value::Value};

pub(crate) fn builtin(args: &[Value], env: &Environment) -> Option<(Value, Environment)> {
    if let [v] = &args[..] {
        match eval_apply(v, env) {
            Some((Value::Number(n), _)) => Some((Value::Number(n.cos()), Environment::new())),
            Some((e, _)) => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::cos]: ",
                        "Only accepts 1 number, but {:?} was passed."
                    ),
                    e
                );
                None
            }
            None => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::cos]: ",
                        "Cannot evaluate expression {:?}."
                    ),
                    v
                );
                None
            }
        }
    } else {
        eprintln!(
            concat!(
                "Error[ksl::builtin::cos]: ",
                "Only accepts 1 argument, but {} were passed."
            ),
            args.len()
        );
        None
    }
}