Скачать или смотреть Understanding Recursion in Erlang: How to Check if a Substring is a Prefix of a String Recursively

Dive into the world of Erlang recursion and learn how to determine if a substring is a prefix of a string using a recursive approach without built-in functions. Read more for a step-by-step breakdown!
---
This video is based on the question https://stackoverflow.com/q/67402469/ asked by the user 'Pfinnn' ( https://stackoverflow.com/u/10927457/ ) and on the answer https://stackoverflow.com/a/67404428/ provided by the user 'Steve Vinoski' ( https://stackoverflow.com/u/409228/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Erlang Understanding recursion: Find if substring is prefix of string recursively

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding Recursion in Erlang: How to Check if a Substring is a Prefix of a String Recursively

When it comes to string manipulation, one common requirement is to check if a substring is a prefix of a larger string. In Erlang, this can be elegantly achieved using recursion, allowing us to explore the string character by character. In this guide, we will dissect an implementation that uses recursion to find if a substring is indeed a prefix, and we'll break down how it works step-by-step.

The Problem Statement

The primary goal is to create a function that will determine if one string is a prefix of another. Specifically, we want to implement this without relying on any built-in list functions, which makes the challenge more interesting and educational for understanding recursion in Erlang.

The Implementation

Here's the implementation of the function that checks for a prefix:

[[See Video to Reveal this Text or Code Snippet]]

How the Function Works

This implementation consists of three clauses which are checked in order:

Matching Prefix Characters:

The first clause checks if the first character of both strings matches. If they do, it recursively calls checkStringPrefix on the tails of both strings.

Empty Lookup String:

The second clause handles the case when the lookup string (the substring) is empty. It indicates that the substring has been fully matched, returning "***".

Non-Matching Cases:

The third clause is executed when the first characters do not match and when the lookup string is not empty. It returns an empty string "", indicating that the prefix check was unsuccessful.

Detailed Breakdown

To clarify how each clause operates, let's analyze various examples:

Example 1: Matching Characters

[[See Video to Reveal this Text or Code Snippet]]

The characters 't', 'e', 's', and 't' match sequentially, so recursion continues until the prefix string becomes empty, leading to a return value of "***".

Example 2: Non-Matching Characters

[[See Video to Reveal this Text or Code Snippet]]

Here, the first characters match at first, but as characters are compared, the extra 't's in the lookup string cause the third clause to trigger, resulting in an empty return value indicating no prefix match.

Understanding Function Calls

When passing various input strings, it's crucial to understand what happens:

When both strings contain letters that match, the function continues, and when the lookup string becomes empty, it calls the second clause, returning "***".

If the first characters mismatch, the function falls through to the third clause, leading to an empty result "".

Recursion Logic Explained

The ordering of function clauses is significant:

The first clause only executes if both the head of the string and the lookup are not empty and match.

The second clause only activates if the lookup string is empty; hence, it signifies that all preceding characters in the prefixed string matched.

The third clause serves as a catch-all for mismatches or remaining characters in the lookup that haven't been validated yet.

Conclusion

In summary, this recursive implementation demonstrates a powerful way to handle string prefix validation in Erlang. By breaking the problem down into recursive calls, we can elegantly navigate through the strings without relying on any built-in list functions. Mastering this kind of recursive logic paves the way for tackling more complex problems in functional programming.

Next time you need to determine if a substring is a prefix, remember to apply these principles of recursion, and you'll find that many similar problems can be approached with the same elegant