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Asked: 2026-06-06T02:32:46+00:00

While studying for a Functional Programming exam, I came across the following question from

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While studying for a Functional Programming exam, I came across the following question from a previous test:

t1 = (reverse . take 2 . words . \ _ -> name)"!"

The task is to write the output of the statement. The variable name refers to the student’s name, written in the form “Smith, John”. If I enter the statement into WinHugs, I get the following output:

["John","Smith,"]

I understand what the functions reverse, take and words are doing and I understand how the . operator connects them. What I don’t understand is what is happening here:

\ _ -> name

What are the slash, underscore and “arrow” for? Also, what does the exclamation point in quotation marks do? (nothing?)

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1 Answer

  1. Editorial Team

    It’s a lambda function that discards its (only) argument (i.e. “!”) and yields name.

    As another lambda example, the following would be a lambda function that squares its argument:

    \x -> x * x

    The \ is the notation used to introduce a lambda function.

    The _ means “variable about whose name we do not care”.

    The -> separates the lambda function’s arguments from the expression used to specify its result.

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