First commitHEADmain

1 files changed, 66 insertions, 0 deletions

diff --git a/src/builtins/pairlists.rs b/src/builtins/pairlists.rs
new file mode 100644
index 0000000..1c18810
--- /dev/null
+++ b/src/builtins/pairlists.rs
@@ -0,0 +1,66 @@
+use std::sync::Arc;
+
+use crate::interpreter::{self, Interpreter, Value};
+
+pub fn pair(interpreter: &mut Interpreter, args: &[Arc<Value>]) -> Arc<Value> {
+	let keys = interpreter
+		.eval(args[0].clone())
+		.list()
+		.expect("a list of keys");
+	let vals = interpreter
+		.eval(args[1].clone())
+		.list()
+		.expect("a list of values");
+
+	let pairs = keys
+		.into_iter()
+		.zip(vals)
+		.map(|(key, value)| Arc::new(Value::Pair(key, value)))
+		.collect::<Box<_>>();
+
+	interpreter::vec_to_value(&pairs)
+}
+
+fn assoc_inner(key: Arc<Value>, pairs: &[Arc<Value>]) -> Option<Arc<Value>> {
+	let get_value = |pair: &Arc<Value>| {
+		if let Value::Pair(k, v) = &**pair {
+			(k == &key).then(|| v.clone())
+		} else {
+			None
+		}
+	};
+
+	pairs.iter().filter_map(get_value).next()
+}
+
+pub fn assoc(interpreter: &mut Interpreter, args: &[Arc<Value>]) -> Arc<Value> {
+	let key = interpreter.eval(args[0].clone());
+	let pairs = interpreter.eval(args[1].clone()).list().expect("a list");
+
+	assoc_inner(key, &pairs).unwrap()
+}
+
+pub fn sublis(interpreter: &mut Interpreter, args: &[Arc<Value>]) -> Arc<Value> {
+	fn sublis_inner(expression: Arc<Value>, replacements: &[Arc<Value>]) -> Arc<Value> {
+		if let Some(value) = assoc_inner(expression.clone(), replacements) {
+			return value.clone();
+		}
+
+		if let Value::Pair(a, b) = &*expression {
+			return Arc::new(Value::Pair(
+				sublis_inner(a.clone(), replacements),
+				sublis_inner(b.clone(), replacements),
+			));
+		}
+
+		expression
+	}
+
+	let expression = interpreter.eval(args[1].clone());
+	let replacements = interpreter
+		.eval(args[0].clone())
+		.list()
+		.expect("a list of replacements");
+
+	sublis_inner(expression, &replacements)
+}