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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 [pred, true_case, false_case] = &args[..] {
match eval_apply(pred, env) {
Some((Value::Atom(p), _)) if &p == TRUE_SYMBOL || &p == FALSE_SYMBOL => {
let eval_case = if &p == TRUE_SYMBOL {
true_case
} else {
false_case
};
match eval_apply(eval_case, env) {
Some((val, new_env)) => Some((val, new_env)),
None => {
eprintln!(
concat!(
"Error[ksl::builtin::if]: ",
"Cannot evaluate expression {:?}."
),
eval_case
);
None
}
}
}
Some((e, _)) => {
eprintln!(
concat!(
"Error[ksl::builtin::if]: ",
"Expected an boolean, but got `{:?}`."
),
e
);
None
}
None => {
eprintln!(
concat!(
"Error[ksl::builtin::if]: ",
"Cannot evaluate expression {:?}."
),
pred
);
None
}
}
} else {
eprintln!(
concat!(
"Error[ksl::builtin::if]: ",
"Only accepts 3 arguments, but {} were passed."
),
args.len()
);
None
}
}