lexer: use Err type for unrecognised tokens instead of unimplemented

src/lexer/error.rs

@@ -16,6 +16,7 @@ pub enum SyntaxError {
     UnpredictableState(Span),
     InvalidDocIndentation(Span),
     InvalidDocBodyIndentationLevel(usize, Span),
+    UnrecognisedToken(u8, Span),
 }
 
 impl Display for SyntaxError {
@@ -72,6 +73,13 @@ impl Display for SyntaxError {
                 expected,
                 span.0
             ),
+            Self::UnrecognisedToken(token, span) => write!(
+                f,
+                "Syntax Error: Unrecognised token {} on line {} column {}",
+                token,
+                span.0,
+                span.1
+            )
         }
     }
 }

src/lexer/mod.rs

@@ -1126,12 +1126,7 @@ impl Lexer {
                 let label = self.consume_identifier(state);
                 TokenKind::Identifier(label.into())
             }
-            &[b, ..] => unimplemented!(
-                "<var offset> char: {}, line: {}, col: {}",
-                b as char,
-                state.span.0,
-                state.span.1
-            ),
+            &[b, ..] => return Err(SyntaxError::UnrecognisedToken(b, state.span)),
             [] => return Err(SyntaxError::UnexpectedEndOfFile(state.span)),
         };
         Ok(Token { kind, span })