ksl 0.1.30

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

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

pub(crate) fn builtin(args: &[Value], env: Environment) -> Result<Value, std::sync::Arc<str>> {
    if let [pred, true_case, false_case] = args {
        match eval_apply(pred, env.clone())? {
            p @ Value::Atom(_) if p == *TRUE_SYMBOL => eval_apply(true_case, env),
            p @ Value::Atom(_) if p == *FALSE_SYMBOL => eval_apply(false_case, env),
            e => Err(std::sync::Arc::from(format!(
                concat!("Error[ksl::builtin::If]: ", "Unexpected value: `{}`."),
                e
            ))),
        }
    } else {
        Err(std::sync::Arc::from(format!(
            concat!(
                "Error[ksl::builtin::If]: ",
                "Expected 3 parameters, but {} were passed."
            ),
            args.len()
        )))
    }
}