diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.2.1.0 -- 2021-01-15
+
+* Add `member` for `EnumSet` / `SymEnumSet`.
+
 ## 0.2.0.0 -- 2021-01-13
 
 * Add `Semigroup` / `Monoid` instances for `EnumSet` / `SymEnumSet`.
diff --git a/src/Language/Lexer/Tlex/Data/EnumSet.hs b/src/Language/Lexer/Tlex/Data/EnumSet.hs
--- a/src/Language/Lexer/Tlex/Data/EnumSet.hs
+++ b/src/Language/Lexer/Tlex/Data/EnumSet.hs
@@ -3,6 +3,7 @@
     empty,
     singleton,
     insert,
+    member,
     union,
     intersection,
     difference,
@@ -41,6 +42,11 @@
     do IntSet.insert
         do fromEnum x
         do s
+
+member :: Enum a => a -> EnumSet a -> Bool
+member x (EnumSet s) = IntSet.member
+    do fromEnum x
+    do s
 
 union :: Enum a => EnumSet a -> EnumSet a -> EnumSet a
 union (EnumSet s1) (EnumSet s2) = EnumSet do IntSet.union s1 s2
diff --git a/src/Language/Lexer/Tlex/Data/SymEnumSet.hs b/src/Language/Lexer/Tlex/Data/SymEnumSet.hs
--- a/src/Language/Lexer/Tlex/Data/SymEnumSet.hs
+++ b/src/Language/Lexer/Tlex/Data/SymEnumSet.hs
@@ -4,6 +4,7 @@
     full,
     complement,
     singleton,
+    member,
     union,
     intersection,
     difference,
@@ -50,6 +51,15 @@
     { isStraight = True
     , internalEnumSet = EnumSet.singleton x
     }
+
+member :: Enum a => a -> SymEnumSet a -> Bool
+member x s = case isStraight s of
+    True ->
+        EnumSet.member x
+            do internalEnumSet s
+    False -> not do
+        EnumSet.member x
+            do internalEnumSet s
 
 union :: Enum a => SymEnumSet a -> SymEnumSet a -> SymEnumSet a
 union s1 s2 = case isStraight s1 of
diff --git a/test/doctest/Doctest.hs b/test/doctest/Doctest.hs
--- a/test/doctest/Doctest.hs
+++ b/test/doctest/Doctest.hs
@@ -3,10 +3,11 @@
 import           Prelude
 
 import qualified Build_doctests     as BuildF
+import qualified Control.Exception  as Exception
 import           Control.Monad
 import qualified System.Environment as IO
 import qualified System.IO          as IO
-import           Test.DocTest       (doctest)
+import qualified Test.DocTest       as DocTest
 
 main :: IO ()
 main = forM_ BuildF.components \(BuildF.Component name flags pkgs sources) -> do
@@ -16,6 +17,7 @@
   IO.hFlush IO.stdout
   let args = flags ++ pkgs ++ sources
   IO.unsetEnv "GHC_ENVIRONMENT"
-  doctest args
+  DocTest.doctest args `Exception.catch`
+    \(e :: Exception.SomeException) -> print e
   putStrLn "============================================="
   IO.hFlush IO.stdout
diff --git a/tlex-core.cabal b/tlex-core.cabal
--- a/tlex-core.cabal
+++ b/tlex-core.cabal
@@ -2,7 +2,7 @@
 build-type:          Custom
 
 name:                tlex-core
-version:             0.2.0.0
+version:             0.2.1.0
 license:             Apache-2.0 OR MPL-2.0
 license-file:        LICENSE
 copyright:           (c) 2021 Mizunashi Mana