Tracks
/
AWK
AWK
/
Exercises
/
List Operations
List Operations

List Operations

Hard

Instructions

Implement basic list operations.

In functional languages list operations like length, map, and reduce are very common. Implement a series of basic list operations, without using existing functions.

The precise number and names of the operations to be implemented will be track dependent to avoid conflicts with existing names, but the general operations you will implement include:

  • append (given two lists, add all items in the second list to the end of the first list);
  • concatenate (given a series of lists, combine all items in all lists into one flattened list);
  • filter (given a predicate and a list, return the list of all items for which predicate(item) is True);
  • length (given a list, return the total number of items within it);
  • map (given a function and a list, return the list of the results of applying function(item) on all items);
  • foldl (given a function, a list, and initial accumulator, fold (reduce) each item into the accumulator from the left using function(accumulator, item));
  • foldr (given a function, a list, and an initial accumulator, fold (reduce) each item into the accumulator from the right using function(item, accumulator));
  • reverse (given a list, return a list with all the original items, but in reversed order);

New AWK concepts

Refer to the matrix exercise instructions to refresh on some interesting GNU awk language features.

Dynamic function invocation

awk functions are not first-class objects: they can't get passed around like some other languages allow. However, a variable can hold the name of a function (a string), and the function is invoked using a special @varname(args) notation. An example:

function greet(name) {
    print "Hello, " name
}
BEGIN {
    greet("John")       # => "Hello, John"

    f = "greet"
    f("Bill")           # => error
    @f("Bill")          # => "Hello, Bill"
}

This is described in Indirect Function Calls. This is a gawk extension.

Last updated 23 November 2022
Edit via GitHub The link opens in a new window or tab
AWK Exercism

Ready to start List Operations?

Sign up to Exercism to learn and master AWK with 58 exercises, and real human mentoring, all for free.