Remove conditional behavior of Future.pure

It was not wrapping awaitable values in a new awaitable, which is
incorrect and confusing behavior.

monads/future.py

@@ -17,15 +17,11 @@ class Future(Monad[T]):
         self.awaitable = awaitable
 
     @classmethod
-    def pure(cls, value: Union[T, Awaitable[T]]) -> Future[T]:
-        if isinstance(value, Awaitable):
-            return Future(value)
-        else:
+    def pure(cls, value: T) -> Future[T]:
+        async def identity(x: T) -> T:
+            return x
 
-            async def identity(x: T) -> T:
-                return x
-
-            return Future(identity(value))
+        return Future(identity(value))
 
     def map(self, function: Callable[[T], S]) -> Future[S]:
         async def map(f: Callable[[T], S], x: Awaitable[T]) -> S:

tests/test_future.py

@@ -28,16 +28,6 @@ async def test_types() -> None:
     await sequence
 
 
-@pytest.mark.asyncio
-async def test_pure_accepts_values_or_awaitables() -> None:
-    async def three() -> int:
-        return 3
-
-    a: Future[int] = Future.pure(3)
-    b: Future[int] = Future.pure(three())
-    assert await a == await b
-
-
 @pytest.mark.asyncio
 async def test_functor_identity() -> None:
     identity: Callable[[int], int] = lambda x: x