diff --git a/lark/lexer.py b/lark/lexer.py
index 3464591..a7e5c26 100644
--- a/lark/lexer.py
+++ b/lark/lexer.py
@@ -12,7 +12,7 @@ import warnings
 try:
     import interegular
 except ImportError:
-    interegular = None
+    pass
 if TYPE_CHECKING:
     from .common import LexerConf
 
@@ -24,10 +24,10 @@ from .grammar import TOKEN_DEFAULT_PRIORITY
 ###{standalone
 from copy import copy
 
-try:  # For the standalone parser, we need to make sure that interegular is set to None to avoid NameErrors later on
-    interegular
+try:  # For the standalone parser, we need to make sure that has_interegular is False to avoid NameErrors later on
+    has_interegular = bool(interegular)
 except NameError:
-    interegular = None
+    has_interegular = False
 
 class Pattern(Serialize, ABC):
 
@@ -490,7 +490,7 @@ class BasicLexer(Lexer):
             if not (set(conf.ignore) <= {t.name for t in terminals}):
                 raise LexError("Ignore terminals are not defined: %s" % (set(conf.ignore) - {t.name for t in terminals}))
 
-            if interegular:
+            if has_interegular:
                 if not comparator:
                     comparator = interegular.Comparator.from_regexes(terminal_to_regexp)
                 for group in classify(terminal_to_regexp, lambda t:t.priority).values():
@@ -592,7 +592,7 @@ class ContextualLexer(Lexer):
         trad_conf = copy(conf)
         trad_conf.terminals = terminals
 
-        if interegular and not conf.skip_validation:
+        if has_interegular and not conf.skip_validation:
             comparator = interegular.Comparator.from_regexes({t: t.pattern.to_regexp() for t in terminals})
         else:
             comparator = None
diff --git a/lark/tools/__init__.py b/lark/tools/__init__.py
index 5daf972..c6995c6 100644
--- a/lark/tools/__init__.py
+++ b/lark/tools/__init__.py
@@ -8,8 +8,9 @@ import warnings
 from lark import Lark, logger
 try:
     from interegular import logger as interegular_logger
+    has_interegular = True
 except ImportError:
-    interegular_logger = None
+    has_interegular = False
 
 lalr_argparser = ArgumentParser(add_help=False, epilog='Look at the Lark documentation for more info on the options')
 
@@ -44,7 +45,7 @@ for flag in flags:
 
 def build_lalr(namespace):
     logger.setLevel((ERROR, WARN, INFO, DEBUG)[min(namespace.verbose, 3)])
-    if interegular_logger is not None:
+    if has_interegular:
         interegular_logger.setLevel(logger.getEffectiveLevel())
     if len(namespace.start) == 0:
         namespace.start.append('start')
diff --git a/lark/utils.py b/lark/utils.py
index 198c352..753610a 100644
--- a/lark/utils.py
+++ b/lark/utils.py
@@ -3,7 +3,7 @@ import os
 from functools import reduce
 from itertools import product
 from collections import deque
-from typing import Callable, Iterator, List, Optional, Tuple, Type, TypeVar, Union, Dict, Any, Sequence
+from typing import Callable, Iterator, List, Optional, Tuple, Type, TypeVar, Union, Dict, Any, Sequence, Iterable
 
 ###{standalone
 import sys, re
@@ -21,7 +21,7 @@ NO_VALUE = object()
 T = TypeVar("T")
 
 
-def classify(seq: Sequence, key: Optional[Callable] = None, value: Optional[Callable] = None) -> Dict:
+def classify(seq: Iterable, key: Optional[Callable] = None, value: Optional[Callable] = None) -> Dict:
     d: Dict[Any, Any] = {}
     for item in seq:
         k = key(item) if (key is not None) else item
diff --git a/test-requirements.txt b/test-requirements.txt
index 85303e9..de2a735 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,3 +1,3 @@
-interegular>=0.2.2
+interegular>=0.2.3
 Js2Py==0.68
 regex
diff --git a/tox.ini b/tox.ini
index 0b1426d..0ca1d45 100644
--- a/tox.ini
+++ b/tox.ini
@@ -23,6 +23,7 @@ skip_install = true
 recreate = false
 deps =
     mypy==0.950
+    interegular>=0.2.3
     types-atomicwrites
     types-regex
     rich