more fixes in DFA minimization and emptiness check

fja_checker.py

 from parser import Parser, ParsingError
-from reg_automata import DFA
+from reg_automata import DFA, State
 from antlr4 import RecognitionException # type: ignore
 import sys
 import signal
@@ -17,7 +17,9 @@ def parse(string: str, automaton_type: str) -> DFA:
         return automaton
 
     except ParsingError as message:
-        print(message)
+        print("Parsing error:", message)
+    except AttributeError as message:
+        print("Parsing error:", message)
 
 
 

reg_automata.py

@@ -409,9 +409,13 @@ class DFA:
 
         if len(reachable.intersection(self.final)) == 0:
             return IsEmptyResult()
+
+        word = []
+        state = reachable.intersection(self.final).pop()
+        if state == self.init:
+            return IsEmptyResult('ε') # TODO some Eps -> str
+
         else:
-            word = []
-            state = reachable.intersection(self.final).pop()
             while state is not self.init:
                 word.append(predecessor[state][1].name)
                 state = predecessor[state][0]