Data commit

Task/Monads-Maybe-monad/Python/monads-maybe-monad.py

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+"""A Maybe Monad. Requires Python >= 3.7 for type hints."""
+from __future__ import annotations
+
+from typing import Any
+from typing import Callable
+from typing import Generic
+from typing import Optional
+from typing import TypeVar
+from typing import Union
+
+
+T = TypeVar("T")
+
+
+class Maybe(Generic[T]):
+    def __init__(self, value: Union[Optional[T], Maybe[T]] = None):
+        if isinstance(value, Maybe):
+            self.value: Optional[T] = value.value
+        else:
+            self.value = value
+
+    def __rshift__(self, func: Callable[[Optional[T]], Maybe[Any]]):
+        return self.bind(func)
+
+    def bind(self, func: Callable[[Optional[T]], Maybe[Any]]) -> Maybe[Any]:
+        return func(self.value)
+
+    def __str__(self):
+        return f"{self.__class__.__name__}({self.value!r})"
+
+
+def plus_one(value: Optional[int]) -> Maybe[int]:
+    if value is not None:
+        return Maybe[int](value + 1)
+    return Maybe[int](None)
+
+
+def currency(value: Optional[int]) -> Maybe[str]:
+    if value is not None:
+        return Maybe[str](f"${value}.00")
+    return Maybe[str](None)
+
+
+if __name__ == "__main__":
+    test_cases = [1, 99, None, 4]
+
+    for case in test_cases:
+        m_int = Maybe[int](case)
+        result = m_int >> plus_one >> currency
+        # or..
+        # result = m_int.bind(plus_one).bind(currency)
+        print(f"{str(case):<4} -> {result}")