Monads/Maybe monad: Difference between revisions
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→ ❌ (#f . 0)
</syntaxhighlight>
=={{header|FreeBASIC}}==
{{trans|Wren}}
<syntaxhighlight lang="vbnet">Type mmaybe
As Integer value
End Type
Function Bindf(m As mmaybe, f As Function(As mmaybe) As mmaybe) As mmaybe
Return f(m)
End Function
Function Unit(i As Integer) As mmaybe
Dim As mmaybe m
m.value = i
Return m
End Function
Function Decrement(mm As mmaybe) As mmaybe
Dim As mmaybe result
result.value = Iif(mm.value = 0, 0, mm.value - 1)
Return Unit(result.value)
End Function
Function Triple(mm As mmaybe) As mmaybe
Dim As mmaybe result
result.value = Iif(mm.value = 0, 0, 3 * mm.value)
Return Unit(result.value)
End Function
Dim As Integer values(3) = {3, 4, 0, 5}
Dim As Function(As mmaybe) As mmaybe Ptr decrementPtr = @Decrement
Dim As Function(As mmaybe) As mmaybe Ptr triplePtr = @Triple
For i As Integer = Lbound(values) To Ubound(values)
Dim As mmaybe m1 = Unit(values(i))
Dim As mmaybe m2 = Bindf(Bindf(m1, decrementPtr), triplePtr)
Dim As String s1 = Iif(m1.value = 0, "none", Str(m1.value))
Dim As String s2 = Iif(m2.value = 0, "none", Str(m2.value))
Print Using "\ \ -> \ \"; s1; s2
Next i
Sleep</syntaxhighlight>
{{out}}
<pre> 3 -> 6
4 -> 9
none -> none
5 -> 12</pre>
=={{header|F_Sharp|F#}}==
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=={{header|Python}}==
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.
<syntaxhighlight lang="python">
"""A Maybe monad. Requires Python >= 3.7 for type hints."""
from __future__ import annotations
from typing import Callable
from typing import Generic
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T = TypeVar("T")
U = TypeVar("U")
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self.value = value
def __rshift__(self, func: Callable[[Optional[T]], Maybe[
return self.bind(func)
def bind(self, func: Callable[[Optional[T]], Maybe[
return func(self.value)
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def plus_one(value: Optional[int]) -> Maybe[int]:
if value is not None:
return Maybe
return Maybe
def currency(value: Optional[int]) -> Maybe[str]:
if value is not None:
return Maybe
return Maybe
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for case in test_cases:
# or..
# result =
print(f"{str(case):<4} -> {result}")
</syntaxhighlight>
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{{trans|Go}}
{{libheader|Wren-fmt}}
<syntaxhighlight lang="
class Maybe {
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var s1 = (m1.value) ? "%(m1.value)" : "none"
var s2 = (m2.value) ? "%(m2.value)" : "none"
}</syntaxhighlight>
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