Add type stubs for Maybe

This allows Maybe[T] to be used as a type.  Both Nothing and Just are
of type Maybe.

* mypy.ini: Add default location for stub files.
* stubs/pymonad/__init__.pyi: New file.
* stubs/pymonad/maybe.pyi: Ditto.

2 files changed, 26 insertions, 0 deletions

diff --git a/stubs/pymonad/__init__.pyi b/stubs/pymonad/__init__.pyi
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/stubs/pymonad/__init__.pyi
diff --git a/stubs/pymonad/maybe.pyi b/stubs/pymonad/maybe.pyi
new file mode 100644
index 0000000..abf1433
--- /dev/null
+++ b/stubs/pymonad/maybe.pyi
@@ -0,0 +1,26 @@
+import pymonad.monad  # type: ignore
+from _typeshed import Incomplete
+from typing import Any, Callable, Generic, TypeVar
+
+S = TypeVar('S')
+T = TypeVar('T')
+
+class Maybe(pymonad.monad.Monad, Generic[T]):
+    @classmethod
+    def insert(cls, value: T) -> Maybe[T]: ...
+    def amap(self, monad_value: Maybe[S]) -> Maybe[T]: ...
+    def bind(self, kleisli_function: Callable[[S], Maybe[T]]) -> Maybe[T]: ...
+    def is_just(self) -> bool: ...
+    def is_nothing(self) -> bool: ...
+    def map(self, function: Callable[[S], T]) -> Maybe[T]: ...
+    def maybe(self, default_value: T, extraction_function: Callable[[S], T]) -> T: ...
+    option: Incomplete
+    def __eq__(self, other): ...
+
+def Just(value: T) -> Maybe[T]: ...
+
+Nothing: Maybe[Any]
+
+class Option(Maybe[T]): ...
+
+def Some(value: T) -> Option[T]: ...