feat(tazjin/rlox): Implement single-character scanning r/1914

... still not that interesting, but at this point slightly divergent
from the book:

The book embraces mutability for interpreter state, initially for
tracking whether an error condition has occured.

I avoid this by instead defining an error type and collecting the
error values, to be handled later on.

Notes: So far nothing special, but this is just the beginning of the
book. I like the style it is written in and it has pointed to some
interesting resources, such as a 1965 paper titled "The Next 700
Languages".

Change-Id: I030b38438fec9eb55372bf547af225138908230a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2144
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI

1 files changed, 14 insertions, 0 deletions

diff --git a/users/tazjin/rlox/src/errors.rs b/users/tazjin/rlox/src/errors.rs
new file mode 100644
index 000000000000..46c739ef2f46
--- /dev/null
+++ b/users/tazjin/rlox/src/errors.rs
@@ -0,0 +1,14 @@
+#[derive(Debug)]
+pub enum ErrorKind {
+    UnexpectedChar(char),
+}
+
+#[derive(Debug)]
+pub struct Error {
+    pub line: usize,
+    pub kind: ErrorKind,
+}
+
+pub fn report(loc: &str, err: &Error) {
+    eprintln!("[line {}] Error {}: {:?}", err.line, loc, err.kind);
+}