From 090c96eae998fd399975e85321189a136a7dbddd Mon Sep 17 00:00:00 2001
From: Vincent Ambo <mail@tazj.in>
Date: Thu, 14 Jan 2021 03:13:51 +0300
Subject: feat(tazjin/rlox): Scaffolding for builtin functions

... and adds an example builtin which returns the current epoch.

The types introduced by this, especially in the interpreter module,
are going to be used for user-defined functions, too.

Change-Id: I0364a67241e94642cde08489ac711a340e30ebe8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2381
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
---
 users/tazjin/rlox/src/interpreter.rs          | 24 ++++++++++++++++++++++++
 users/tazjin/rlox/src/interpreter/builtins.rs | 25 +++++++++++++++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 users/tazjin/rlox/src/interpreter/builtins.rs

(limited to 'users/tazjin')

diff --git a/users/tazjin/rlox/src/interpreter.rs b/users/tazjin/rlox/src/interpreter.rs
index b59034ea970c..5e2eba02d460 100644
--- a/users/tazjin/rlox/src/interpreter.rs
+++ b/users/tazjin/rlox/src/interpreter.rs
@@ -5,8 +5,32 @@ use std::collections::HashMap;
 use std::rc::Rc;
 use std::sync::RwLock;
 
+// Implementation of built-in functions.
+mod builtins;
+
 // Tree-walk interpreter
 
+// Representation of all callables, including builtins & user-defined
+// functions.
+#[derive(Clone, Debug)]
+pub enum Callable {
+    Builtin(&'static dyn builtins::Builtin),
+}
+
+impl Callable {
+    fn arity(&self) -> usize {
+        match self {
+            Callable::Builtin(builtin) => builtin.arity(),
+        }
+    }
+
+    fn call(&self, args: Vec<Value>) -> Result<Value, Error> {
+        match self {
+            Callable::Builtin(builtin) => builtin.call(args),
+        }
+    }
+}
+
 // Representation of an in-language value.
 #[derive(Clone, Debug)]
 enum Value {
diff --git a/users/tazjin/rlox/src/interpreter/builtins.rs b/users/tazjin/rlox/src/interpreter/builtins.rs
new file mode 100644
index 000000000000..6ed9f07c3ffa
--- /dev/null
+++ b/users/tazjin/rlox/src/interpreter/builtins.rs
@@ -0,0 +1,25 @@
+use std::fmt;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::errors::Error;
+use crate::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)))
+    }
+}
-- 
cgit 1.4.1