Flesh out grammar for parsing labels

src/labels/labels.rs

@@ -1,12 +1,25 @@
 use crate::{
-    preprocess::peg::{EOF, Rule, Star},
+    preprocess::peg::{Alt, And, Dot, EOF, Not, Opt, Rule, Star},
     star,
 };
 
 fn parse_program() -> impl Rule {
-    (star!(parse_line), EOF)
+    (Opt((parse_line, star!(("\n", parse_line)))), EOF)
 }
 
 fn parse_line() -> impl Rule {
-    (star!("foo"), "\n")
+    Alt((parse_label_line, parse_any_line))
+}
+
+fn parse_any_line() -> impl Rule {
+    (star!(Not("\n"), Dot), eol)
+}
+
+fn parse_label_line() -> impl Rule {
+    let allowed = Alt(('A'..='Z', 'a'..='z', '0'..='9', "_", "@", "~"));
+    (":", star!(allowed), eol)
+}
+
+fn eol() -> impl Rule {
+    Alt((And("\n"), EOF))
 }