Add const Nothing instance.

src/maybe/__init__.py

@@ -1,5 +1,6 @@
 from .maybe import (
     Nothing,
+    NOTHING,
     Some,
     SomeNothing,
     Maybe,
@@ -10,6 +11,7 @@
 
 __all__ = [
     "Nothing",
+    "NOTHING",
     "Some",
     "SomeNothing",
     "Maybe",

src/maybe/maybe.py

@@ -289,6 +289,7 @@ def ok_or_else(self, op: Callable[[], E]) -> result.Err[E]:
             """
             return result.Err(op())
 
+NOTHING = Nothing()
 
 # Define Maybe as a generic type alias for use in type annotations
 Maybe: TypeAlias = Union[Some[T], Nothing]

tests/test_maybe.py

@@ -2,6 +2,7 @@
 
 from typing import Callable
 
+from maybe.maybe import NOTHING
 import pytest
 import result
 
@@ -29,7 +30,12 @@ def test_eq() -> None:
     assert Some(1) != "abc"
     assert Some("0") != Some(0)
 
-
+def test_const_nothing() -> None:
+    assert NOTHING == Nothing()
+    assert NOTHING.is_nothing() is True
+    assert Some(1) != NOTHING
+    assert len({Some(1), NOTHING}) == 2
+
 def test_hash() -> None:
     assert len({Some(1), Nothing(), Some(1), Nothing()}) == 2
     assert len({Some(1), Some(2)}) == 2