Initial data commit

Task/Monads-List-monad/Python/monads-list-monad.py

@@ -0,0 +1,60 @@
+"""A List Monad. Requires Python >= 3.7 for type hints."""
+from __future__ import annotations
+from itertools import chain
+
+from typing import Any
+from typing import Callable
+from typing import Iterable
+from typing import List
+from typing import TypeVar
+
+
+T = TypeVar("T")
+
+
+class MList(List[T]):
+    @classmethod
+    def unit(cls, value: Iterable[T]) -> MList[T]:
+        return cls(value)
+
+    def bind(self, func: Callable[[T], MList[Any]]) -> MList[Any]:
+        return MList(chain.from_iterable(map(func, self)))
+
+    def __rshift__(self, func: Callable[[T], MList[Any]]) -> MList[Any]:
+        return self.bind(func)
+
+
+if __name__ == "__main__":
+    # Chained int and string functions
+    print(
+        MList([1, 99, 4])
+        .bind(lambda val: MList([val + 1]))
+        .bind(lambda val: MList([f"${val}.00"]))
+    )
+
+    # Same, but using `>>` as the bind operator.
+    print(
+        MList([1, 99, 4])
+        >> (lambda val: MList([val + 1]))
+        >> (lambda val: MList([f"${val}.00"]))
+    )
+
+    # Cartesian product of [1..5] and [6..10]
+    print(
+        MList(range(1, 6)).bind(
+            lambda x: MList(range(6, 11)).bind(lambda y: MList([(x, y)]))
+        )
+    )
+
+    # Pythagorean triples with elements between 1 and 25
+    print(
+        MList(range(1, 26)).bind(
+            lambda x: MList(range(x + 1, 26)).bind(
+                lambda y: MList(range(y + 1, 26)).bind(
+                    lambda z: MList([(x, y, z)])
+                    if x * x + y * y == z * z
+                    else MList([])
+                )
+            )
+        )
+    )