Underscore syntax

Filter, Map and other nuts that take a function as argument often use only very simple expressions. For instance, the following code extracts all number greater than five within range zero to nine:

>>> from nutsflow import *

>>> Range(10) >> Filter(lambda x: x > 5) >> Collect()
[6, 7, 8, 9]

For such simple expressions nuts-flow provides a special underscore notation, borrowed from Scala, which results in shorter, more readable code

>>> from nutsflow import _

>>> Range(10) >> Filter(_ > 5) >> Collect()
[6, 7, 8, 9]

This is equivalent to

>>> Range(10) >> Filter(lambda _: _ > 5) >> Collect()
[6, 7, 8, 9]

but eliminates the need for the lambda keyword and its arguments. Note that the _ must be imported explicitly, since it is also commonly used in Python as a placeholder for unused variables.

In contrast to lambda functions or Scala’s underscore the, underscore notation in nuts-flow is very limited and only supports expressions with arity one, e.g. _ + 1, _ <= 3, _ == 5, _[0], … More complex or nested expressions such as _ + _, _ > 5 and _ < 10 or len(_) are currently not permitted.