[v3] Implement new Concept Exercise: strings

[TheLostLambda]

This document describes how to implement the strings concept exercise for the Common Lisp track.

Please also watch the following video:

• The Anatomy of a Concept Exercise.

Goal

The goal of this exercise is to familiarise students with strings in Common Lisp and some of the functions for creating and manipulating them (including the relevant sequence functions).

Additionally, the student should be taught how to print values to both strings and the standard output. The focus should be on non-format printing functions, as format is a complex topic for another set of exercises.

Learning objectives

• Be able to write string literals using quotes: "
• Know how to compare strings for equality and order (string=, etc.)
• Know how to trim characters from the ends of a string using string-trim
• Be able to control string case with string-upcase, string-downcase, etc.
• Understand how to concatenate strings with concatentate
• Be able to extract sub-strings with subseq
• Know how to search a string with find, find-if, position, search, etc.
• Be able to get the length of a string with length
• Be able to print objects to the standard output using print
• Be able to convert objects to a string using write-to-string

Out of scope

• Looping through the characters of a string with map or loop
• String formatting with format or other forms of "pretty-printing"
• A exploration of the sequence hierarchy, arrays, or vectors
• String designators or converting from strings to symbols
• Sequence functions that are less meaningful for strings reduce, merge, etc
• The dynamic *standard-output* variable and other built-in printing variables
• Streams and stream functions

Concepts

• strings
• printing

Prerequisites

• expressions
• sameness

Resources to refer to

• http://www.gigamonkeys.com/book/numbers-characters-and-strings.html

Hints

• https://lispcookbook.github.io/cl-cookbook/strings.html

After

More human-friendly print functions could be mentioned (princ, terpri, etc.)

Representer

• Currently, no extra logic needs to be added to the representer.

Analyzer

• Currently, no extra logic needs to be added to the analyzer.

Implementing

Printing can be mentioned as a debugging technique for the online test-runners, but isn't a large focus here. The focus should be on doing something interesting with string manipulation.

Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.

[verdammelt]

This looks good. There are a lot of functions to talk about here - but I think it will give the student a good foundation of strings.

[TheLostLambda]

It is a bit big. I agrees they are good to include, but we can always look into splitting things up if implementing the exercise becomes difficult!

[verdammelt]

There are a few possible seams to split along, perhaps splitting off searching, splitting off printing...

But I think we should leave that to implementation - like you said - we can split it up if it is too hard.