Merge pull request EbookFoundation#1645 from gildo/patch-2

Update free-programming-books.md

Author: vhf

free-programming-books.md

@@ -561,7 +561,7 @@ Original Source: [List of freely available programming books](http://web.archive
 #### Programming Paradigms
 * [Introduction to Functional Programming](http://www.cl.cam.ac.uk/teaching/Lectures/funprog-jrh-1996/) (class lectures and slides)
 * [Type Theory and Functional Programming](https://www.cs.kent.ac.uk/people/staff/sjt/TTFP/)
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+* [Mostly Adequate Guide to Functional Programming](https://drboolean.gitbooks.io/mostly-adequate-guide/)
 
 #### Regular Expressions
 * [Learn Regex The Hard Way](http://regex.learncodethehardway.org/book/) - Zed. A. Shaw