Ensure all monoids and monoids implement their appropriate operators

monads/functor.py

@@ -8,3 +8,5 @@ S = TypeVar("S")
 class Functor(Generic[T]):
     def map(self, function: Callable[[T], S]) -> Functor[S]:  # pragma: no cover
         raise NotImplementedError
+
+    __mul__ = __rmul__ = map

monads/list.py

@@ -34,3 +34,5 @@ class List(Monad[T], Monoidal[list]):
         return List(self.value + other.value)
 
     __add__ = mappend
+    __mul__ = __rmul__ = map
+    __rshift__ = bind

monads/monad.py

@@ -15,3 +15,5 @@ class Monad(Applicative[T]):
     # https://github.com/python/mypy/issues/1317
     def bind(self, function: Callable[[T], Any]) -> Monad[S]:  # pragma: no cover
         raise NotImplementedError
+
+    __rshift__ = bind

monads/reader.py

@@ -43,6 +43,9 @@ class Reader(Monad[T], Generic[Env, T]):
         name = self.function.__name__
         return f"<Reader {module}.{name}>"
 
+    __mul__ = __rmul__ = map
+    __rshift__ = bind
+
 
 class Curried(Reader[Env, T]):
     def __call__(self, *args):

tests/test_functors.py

@@ -19,3 +19,15 @@ def test_associativity(monad) -> None:
     g: Callable[[int], str] = lambda x: str(x)
     m: Functor = monad.pure(3)
     assert m.map(lambda x: g(f(x))) == m.map(f).map(g)
+
+
+def test_map_mul_operator(monad) -> None:
+    m: Functor = monad.pure(3)
+    identity: Callable[[T], T] = lambda x: x
+    assert m.map(identity) == m * identity
+
+
+def test_map_rmul_operator(monad) -> None:
+    m: Functor = monad.pure(3)
+    identity: Callable[[T], T] = lambda x: x
+    assert m.map(identity) == identity * m

tests/test_monads.py

@@ -1,3 +1,5 @@
+from typing import Callable
+
 import pytest  # type: ignore
 
 from monads import Monad
@@ -9,6 +11,12 @@ def test_bind(monad) -> None:
     assert expected == monad.pure(1).bind(lambda x: monad.pure(x + 1))
 
 
+def test_bind_rshift_operator(monad) -> None:
+    m: Monad[int] = monad.pure(2)
+    f: Callable[[int], Monad[int]] = lambda x: monad.pure(x + 1)
+    assert m.bind(f) == m >> f
+
+
 def test_left_identity(monad) -> None:
     n: int = 3
 

tests/test_monoids.py

@@ -28,6 +28,12 @@ def construct(constructor: Constructor, value: Any) -> Monoid:
     return cls(builder(value))
 
 
+def test_mappend_add_operator(constructor: Constructor) -> None:
+    a: Monoid = construct(constructor, 1)
+    b: Monoid = construct(constructor, 2)
+    assert a.mappend(b) == a + b
+
+
 def test_associative(constructor: Constructor) -> None:
     a: Monoid = construct(constructor, 1)
     b: Monoid = construct(constructor, 2)

tests/test_reader.py

@@ -21,6 +21,18 @@ def test_functor_associativity() -> None:
     assert m.map(lambda x: g(f(x)))(0) == m.map(f).map(g)(0)
 
 
+def test_functor_map_mul_operator() -> None:
+    m: Reader = Reader.pure(3)
+    identity: Callable[[T], T] = lambda x: x
+    assert m.map(identity)(0) == (m * identity)(0)
+
+
+def test_functor_map_rmul_operator() -> None:
+    m: Reader = Reader.pure(3)
+    identity: Callable[[T], T] = lambda x: x
+    assert m.map(identity)(0) == (identity * m)(0)
+
+
 def test_applicative_fmap_using_ap() -> None:
     f: Callable[[int], int] = lambda x: x + 1
     m: Reader[int, int] = Reader.pure(3)
@@ -33,6 +45,12 @@ def test_monad_bind() -> None:
     assert expected(0) == m.bind(lambda x: Reader.pure(x + 1))(0)
 
 
+def test_monad_bind_rshift_operator() -> None:
+    m: Reader[int, int] = Reader.pure(2)
+    f: Callable[[int], Reader[int, int]] = lambda x: Reader.pure(x + 1)
+    assert m.bind(f)(0) == (m >> f)(0)
+
+
 def test_monad_left_identity() -> None:
     n: int = 3