Source code for pymonad.operators.state

# --------------------------------------------------------
# (c) Copyright 2014, 2020 by Jason DeLaat.
# Licensed under BSD 3-clause licence.
# --------------------------------------------------------
""" Adds operators to the State monad. """
from typing import Callable, Tuple, TypeVar

import pymonad.monad
import pymonad.operators.operators
import pymonad.state

S = TypeVar("S")  # pylint: disable=invalid-name
T = TypeVar("T")  # pylint: disable=invalid-name


class _State(
    pymonad.operators.operators.MonadOperators, pymonad.state._State[S, T]
):  # pylint: disable=protected-access
    """ See pymonad.operators.operators and pymonad.state. """


def State(
    state_function: Callable[[S], Tuple[T, S]]
) -> _State[S, T]:  # pylint: disable=invalid-name
    """ The State monad constructor function.

    Args:
        state_function: a function with type State -> (Any, State)

    Returns:
        An instance of the State monad.
    """
    return _State(lambda s: state_function(s)[0], lambda s: state_function(s)[1])


State.apply = _State.apply
State.insert = _State.insert