WIP: Reader

monads/__init__.py

@@ -3,3 +3,4 @@ from .applicative import Applicative
 from .monad import Monad
 from .maybe import Maybe, Just, Nothing
 from .result import Result, Ok, Err
+from .reader import Reader

monads/reader.py

@@ -0,0 +1,16 @@
+from __future__ import annotations
+from typing import Any, Callable, Generic, TypeVar
+
+from .monad import Monad
+
+T = TypeVar("T")
+S = TypeVar("S")
+F = Callable[[T], S]
+
+
+class Reader(Monad[T]):
+    def __init__(self, function: F) -> None:
+        self.function = function
+
+    def map(self, function: F) -> Reader:
+        return Reader(lambda x: function(self.function(x)))