Interpreter - clock() native function

src/interpreter/native_fn.rs

@@ -0,0 +1,44 @@
+use std::{
+    cell::RefCell,
+    rc::Rc,
+    time::{SystemTime, UNIX_EPOCH},
+};
+
+use crate::errors::InterpreterError;
+
+use super::{Callable, CallableRef, EnvironmentRef, Value};
+
+/* ----------- *
+ *   clock()   *
+ * ----------- */
+
+#[derive(Debug)]
+struct Clock;
+
+impl Callable for Clock {
+    fn arity(&self) -> usize {
+        0
+    }
+
+    fn call(
+        &self,
+        _environment: &EnvironmentRef,
+        _arguments: Vec<Value>,
+    ) -> Result<Value, InterpreterError> {
+        let now = SystemTime::now();
+        let since_epoch = now
+            .duration_since(UNIX_EPOCH)
+            .expect("looks like it's 2038 already");
+        Ok(Value::Number((since_epoch.as_millis() as f64) / 1000.0))
+    }
+}
+
+impl ToString for Clock {
+    fn to_string(&self) -> String {
+        "<native function clock()>".to_owned()
+    }
+}
+
+pub(crate) fn clock() -> CallableRef {
+    Rc::new(RefCell::new(Clock {}))
+}