refactor(tazjin/rlox): Move treewalk interpreter into subdirectory r/2120

Change-Id: I9163f75db5a1ff75e1b1f81bad78fd9d8ddb104a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2409
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

2 files changed, 126 insertions, 0 deletions

diff --git a/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs b/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs
new file mode 100644
index 000000000000..614f30ff3b23
--- /dev/null
+++ b/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs
@@ -0,0 +1,25 @@
+use std::fmt;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::errors::Error;
+use crate::treewalk::interpreter::Value;
+use crate::parser::Literal;
+
+pub trait Builtin: fmt::Debug {
+    fn arity(&self) -> usize;
+    fn call(&self, args: Vec<Value>) -> Result<Value, Error>;
+}
+
+// Builtin to return the current timestamp.
+#[derive(Debug)]
+pub struct Clock {}
+impl Builtin for Clock {
+    fn arity(&self) -> usize {
+        0
+    }
+
+    fn call(&self, _args: Vec<Value>) -> Result<Value, Error> {
+        let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
+        Ok(Value::Literal(Literal::Number(now.as_secs() as f64)))
+    }
+}
diff --git a/users/tazjin/rlox/src/treewalk/interpreter/tests.rs b/users/tazjin/rlox/src/treewalk/interpreter/tests.rs
new file mode 100644
index 000000000000..34b1df34b0b6
--- /dev/null
+++ b/users/tazjin/rlox/src/treewalk/interpreter/tests.rs
@@ -0,0 +1,101 @@
+use super::*;
+
+/// Evaluate a code snippet, returning a value.
+fn parse_eval(code: &str) -> Value {
+    let chars: Vec<char> = code.chars().collect();
+    let tokens = scanner::scan(&chars).expect("could not scan code");
+    let program = parser::parse(tokens).expect("could not parse code");
+
+    Interpreter::create()
+        .interpret(program)
+        .expect("could not eval code")
+}
+
+#[test]
+fn test_if() {
+    let result = parse_eval(
+        r#"
+if (42 > 23)
+  "pass";
+else
+  "fail";
+"#,
+    );
+
+    assert_eq!(Value::Literal(Literal::String("pass".into())), result,);
+}
+
+#[test]
+fn test_scope() {
+    let result = parse_eval(
+        r#"
+var result = "";
+
+var a = "global a, ";
+var b = "global b, ";
+var c = "global c";
+
+{
+  var a = "outer a, ";
+  var b = "outer b, ";
+
+  {
+    var a = "inner a, ";
+    result = a + b + c;
+  }
+}
+"#,
+    );
+
+    assert_eq!(
+        Value::Literal(Literal::String("inner a, outer b, global c".into())),
+        result,
+    );
+}
+
+#[test]
+fn test_binary_operators() {
+    assert_eq!(Value::Literal(Literal::Number(42.0)), parse_eval("40 + 2;"));
+
+    assert_eq!(
+        Value::Literal(Literal::String("foobar".into())),
+        parse_eval("\"foo\" + \"bar\";")
+    );
+}
+
+#[test]
+fn test_functions() {
+    let result = parse_eval(
+        r#"
+fun add(a, b, c) {
+  a + b + c;
+}
+
+add(1, 2, 3);
+"#,
+    );
+
+    assert_eq!(Value::Literal(Literal::Number(6.0)), result);
+}
+
+#[test]
+fn test_closure() {
+    let result = parse_eval(
+        r#"
+fun makeCounter() {
+  var i = 0;
+  fun count() {
+    i = i + 1;
+  }
+
+  return count;
+}
+
+var counter = makeCounter();
+counter(); // "1".
+counter(); // "2".
+"#,
+    );
+
+    assert_eq!(Value::Literal(Literal::Number(2.0)), result);
+}