Monads/Maybe monad: Difference between revisions
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m (→{{header|Python}}: Improve type hints) |
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=={{header|Python}}== |
=={{header|Python}}== |
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The <code>Maybe</code> class constructor is effectively the <code>unit</code> function. Note that I've used <code>>></code> as the bind operator. Trying to chain <code>__irshift__</code> (<code>>>=</code>) would be a syntax error. |
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In this implementation, a <code>Maybe</code> type's constructor is effectively |
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the <code>unit</code> function. Note that I've used <code>>></code> as the bind |
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operator. Trying to chain <code>__irshift__</code> (<code>>>=</code>) would be a |
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syntax error. |
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<syntaxhighlight lang="python"> |
<syntaxhighlight lang="python"> |
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"""A Maybe monad. Requires Python >= 3.7 for type hints.""" |
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from __future__ import annotations |
from __future__ import annotations |
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from typing import Any |
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from typing import Callable |
from typing import Callable |
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from typing import Generic |
from typing import Generic |
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T = TypeVar("T") |
T = TypeVar("T") |
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U = TypeVar("U") |
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self.value = value |
self.value = value |
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def __rshift__(self, func: Callable[[Optional[T]], Maybe[ |
def __rshift__(self, func: Callable[[Optional[T]], Maybe[U]]) -> Maybe[U]: |
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return self.bind(func) |
return self.bind(func) |
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def bind(self, func: Callable[[Optional[T]], Maybe[ |
def bind(self, func: Callable[[Optional[T]], Maybe[U]]) -> Maybe[U]: |
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return func(self.value) |
return func(self.value) |
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def plus_one(value: Optional[int]) -> Maybe[int]: |
def plus_one(value: Optional[int]) -> Maybe[int]: |
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if value is not None: |
if value is not None: |
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return Maybe |
return Maybe(value + 1) |
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return Maybe |
return Maybe(None) |
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def currency(value: Optional[int]) -> Maybe[str]: |
def currency(value: Optional[int]) -> Maybe[str]: |
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if value is not None: |
if value is not None: |
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return Maybe |
return Maybe(f"${value}.00") |
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return Maybe |
return Maybe(None) |
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for case in test_cases: |
for case in test_cases: |
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result = Maybe(case) >> plus_one >> currency |
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result = m_int >> plus_one >> currency |
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# or.. |
# or.. |
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# result = |
# result = Maybe(case).bind(plus_one).bind(currency) |
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print(f"{str(case):<4} -> {result}") |
print(f"{str(case):<4} -> {result}") |
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</syntaxhighlight> |
</syntaxhighlight> |
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