feat: expression

pkg/saccharine/tokenizer.go

@@ -69,7 +69,7 @@ func getToken(i *iterator.Iterator[rune]) (*token.Token, error) {
 		return token.NewAtom(string(atom), index), nil
 	}
 
-	return nil, fmt.Errorf("unknown character '%v'", letter)
+	return nil, fmt.Errorf("unknown character '%v'", string(letter))
 }
 
 // Parses a list of runes into tokens. All error encountered are returned, as well.