I seem to have solved the infinite loop issue by moving the exit check into the plain list parser.

src/parser/util.rs

@@ -4,6 +4,7 @@ use nom::character::complete::none_of;
 use nom::character::complete::space0;
 use nom::combinator::eof;
 use nom::combinator::not;
+use nom::combinator::peek;
 use nom::combinator::recognize;
 use nom::multi::many0;
 use nom::sequence::tuple;
@@ -106,6 +107,14 @@ pub fn non_whitespace_character(input: &str) -> Res<&str, char> {
     none_of(" \t\r\n")(input)
 }
 
+/// Check that we are at the start of a line
+pub fn exit_matcher_parser<'r, 's>(
+    context: Context<'r, 's>,
+    input: &'s str,
+) -> Res<&'s str, &'s str> {
+    peek(|i| context.check_exit_matcher(i))(input)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;