20 lines
468 B
Markdown
20 lines
468 B
Markdown
---
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title: when
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tags: function,intermediate
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---
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Tests a value, `x`, against a testing function, conditionally applying a function.
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- Check if the value of `predicate(x)` is `True` and if so return `when_true(x)`, otherwise return `x`.
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```py
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def when(predicate, when_true):
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return lambda x: when_true(x) if predicate(x) else x
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```
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```py
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double_even_numbers = when(lambda x: x % 2 == 0, lambda x : x * 2)
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double_even_numbers(2) # 4
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double_even_numbers(1) # 1
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```
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