ksl 0.1.5

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

pub(crate) fn builtin(args: &[Value], env: &Environment) -> Option<(Value, Environment)> {
    if let [v1, v2] = &args[..] {
        match (eval_apply(v1, env), eval_apply(v2, env)) {
            (Some((Value::Number(n1), _)), Some((Value::Number(n2), _))) => Some((
                Value::Atom(String::from(if n1 < n2 {
                    TRUE_SYMBOL
                } else {
                    FALSE_SYMBOL
                })),
                Environment::new(),
            )),
            (Some((e1, _)), Some((e2, _))) => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::less]: ",
                        "Only accepts 2 numbers, but {:?} was passed."
                    ),
                    (e1, e2)
                );
                None
            }
            _ => {
                eprintln!(
                    concat!(
                        "Error[ksl::builtin::less]: ",
                        "Cannot evaluate expression {:?}."
                    ),
                    (v1, v2)
                );
                None
            }
        }
    } else {
        eprintln!(
            concat!(
                "Error[ksl::builtin::less]: ",
                "Only accepts 2 arguments, but {} were passed."
            ),
            args.len()
        );
        None
    }
}