ksl 0.1.30

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

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_expr, body_expr] = args {
        loop {
            let condition = eval_apply(pred_expr, env.clone())?;
            match condition {
                p @ Value::Atom(_) if p == *TRUE_SYMBOL => {
                    let _ = eval_apply(body_expr, env.clone())?;
                }
                p @ Value::Atom(_) if p == *FALSE_SYMBOL => break,
                e => {
                    return Err(std::sync::Arc::from(format!(
                        concat!(
                            "Error[ksl::builtin::While]: ",
                            "Expected a boolean as condition, but got `{}`."
                        ),
                        e
                    )));
                }
            }
        }
        Ok(Value::Unit)
    } else {
        Err(std::sync::Arc::from(format!(
            concat!(
                "Error[ksl::builtin::While]: ",
                "Expected 2 parameters, but {} were passed."
            ),
            args.len()
        )))
    }
}