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Maybe

Maybe

Source code in opskrift/maybe.py 
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class Maybe:
    def __init__(self, value: Optional[a], err: Optional[Exception] = None):
        self.value = value
        self.err = err

    @classmethod
    def unit(cls, *args, **kwargs) -> "Maybe":
        return cls(*args, **kwargs)

    def unwrap(self) -> a | Exception:
        if self.value is not None:
            assert self.err is None
            return self.value
        else:
            assert self.err is not None
            return self.err

    def bind(self, func: Callable) -> "Maybe":
        """
        Call `func` on the wrapped value, storing and propagating the exception if any.
        This has the effect of "fail-on-first-error".

        Similar to Haskell's `(>>=) :: Monad m => m a -> (a -> m b) -> m b`
        """
        if self.value is None:
            return self

        try:
            return Maybe(func(self.value), err=None)
        except Exception as e:
            return Maybe(value=None, err=e)

    def __str__(self):
        if self.value is None:
            if self.err is not None:
                return f"Except ({self.err})"
            else:
                return "Nothing"
        return f"Just ({self.value})"

    __repr__ = __str__

bind(func: Callable) -> 'Maybe'

Call func on the wrapped value, storing and propagating the exception if any. This has the effect of "fail-on-first-error".

Similar to Haskell's (>>=) :: Monad m => m a -> (a -> m b) -> m b

Source code in opskrift/maybe.py 
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def bind(self, func: Callable) -> "Maybe":
    """
    Call `func` on the wrapped value, storing and propagating the exception if any.
    This has the effect of "fail-on-first-error".

    Similar to Haskell's `(>>=) :: Monad m => m a -> (a -> m b) -> m b`
    """
    if self.value is None:
        return self

    try:
        return Maybe(func(self.value), err=None)
    except Exception as e:
        return Maybe(value=None, err=e)