feat(tazjin/rlox): Add basic program structure r/1913

... as well as a Nix derivation, because why not.

Change-Id: Iaf2591ab72676fe0732c3f807b3aa0cff13fb4ef
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2143
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

2 files changed, 31 insertions, 10 deletions

diff --git a/users/tazjin/rlox/src/interpreter.rs b/users/tazjin/rlox/src/interpreter.rs
new file mode 100644
index 000000000000..6a7687c2685e
--- /dev/null
+++ b/users/tazjin/rlox/src/interpreter.rs
@@ -0,0 +1,4 @@
+// Run some Lox code and print it to stdout
+pub fn run(_code: &str) {
+    println!("no interpreter yet, sorry")
+}
diff --git a/users/tazjin/rlox/src/main.rs b/users/tazjin/rlox/src/main.rs
index 3f173673a177..83d220c81631 100644
--- a/users/tazjin/rlox/src/main.rs
+++ b/users/tazjin/rlox/src/main.rs
@@ -1,23 +1,40 @@
-use std::process;
 use std::env;
+use std::fs;
+use std::io;
+use std::io::Write;
+use std::process;
 
-fn run_file(_file: &str) {
-    unimplemented!("no file support yet")
-}
-
-fn run_prompt() {
-    unimplemented!("no prompt support yet")
-}
+mod interpreter;
 
 fn main() {
     let mut args = env::args();
 
-    if args.len() > 1 {
+    if args.len() > 2 {
         println!("Usage: rlox [script]");
         process::exit(1);
-    } else if let Some(file) = args.next() {
+    } else if let Some(file) = args.nth(1) {
         run_file(&file);
     } else {
         run_prompt();
     }
 }
+
+// Run Lox code from a file and print results to stdout
+fn run_file(file: &str) {
+    let contents = fs::read_to_string(file).expect("failed to read the input file");
+    interpreter::run(&contents);
+}
+
+// Evaluate Lox code interactively in a shitty REPL.
+fn run_prompt() {
+    let mut line = String::new();
+
+    loop {
+        print!("> ");
+        io::stdout().flush().unwrap();
+        io::stdin()
+            .read_line(&mut line)
+            .expect("failed to read user input");
+        interpreter::run(&line);
+    }
+}