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First off, for those readers who aren’t programmers, it’s important to define what are the (in)famous regular expressions. According to the Regex Crossword FAQ…

A regular expression (regex or regexp for short) is a special text string for describing a search pattern. (…) For example, if you wanted to find all references to the name "Casper" but using all the different ways of spelling it, you could use the regular expression [CK]asp[ae]r, which will match both "Casper", "Caspar", "Kasper" and "Kaspar".

The thing is: this definition by no means reflects how insanely difficult it is to learn them. There is no other way than repeatedly using them until you eventually start memorizing them, a process that is particularly arduous and unintuitive. This is what Regex Crossword aims to prevent, by hosting a series of Sudoku-like puzzles to help you master them; it won’t be an easy process still, but at least it may be more fun…

On the left you can see a typical puzzle, in which you must carefully  observe the regexs that represent every row or column, and write a letter from a selected list that matches both criteria. You can always press the "Help" button at the top right of the website to visualize a diagram with all the information you need. As you can see, it’s easy to understand the rules, but hard to master them.

The website features several sections to make the levels as varied as possible. There is also another area which includes levels made by other users, along with a stats page. Also, if you check the Help and FAQ section, you will be recommended other tools and online resources in case you want to learn a bit more about regexs. Don’t forget to use an account so that your progress on the levels can be saved.

Finally, although this project is "something we do for fun", you can donate via PayPal or several cryptocurrencies (check the Help and FAQ section to see which ones are available) to help with hosting expenses and to keep ensuring further improvements and levels.

Visit Regex Crossword via the following link.

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Seegras 2 April 2020 at 6:58 am UTC
Doesn't make sense. I'm better with Regex than with Sudoku.
no_information_here 2 April 2020 at 8:32 am UTC
Looks brilliant. I have managed to mostly avoid learning regex so far. This is a good way to learn.
Dunc 2 April 2020 at 12:47 pm UTC
Purple Library GuyWeird. The definition sounds like a straightforward, fairly intuitive thing. What makes them so hard?

The infinity combinations you can get and that they aren't easy to read. IMO is one of the most powerful tool for text search but also a dangerous one (the day you create your RE it totally makes sense and it is hyper intuitive... six weeks later you want to cry).
There are some things in life that are easy to understand, and there are some things that are difficult. The really tricky ones are those that you think you understand perfectly, but it turns out you couldn't be more wrong. Regexes are like that for me. The rules all make perfect logical sense, but whenever I try to follow them I come up with something that totally fails to work as expected.

Fortunately, we have things like txt2regex. (The output from which always leaves me saying, “But that's what I did! Isn't it?”. Oh, well. It works.)
Pangaea 2 April 2020 at 1:18 pm UTC
This looks interesting. I have to check it out. Regex is finicky as all hell. The rules are simple enough really, but the syntax ends up looking totally bonkers. And regex has a really nasty habit of doing stuff you don't expect. Like replacing way too much text.

This is pretty straighforward as far as regex goes, but I'm struggling with crap like this while editing a wiki. Not least because I need about 50 rules probably, not all looking like this. So yeah, a million things can go wrong. Thankfully there are excellent sites such as (LOVE the cheatsheet on the left), that make it a bit more tolerable.

Philadelphus 4 April 2020 at 12:44 am UTC
This looks really interesting, I'll have to give it a shot! Always good to get more practice with regexes.

Purple Library GuyWeird. The definition sounds like a straightforward, fairly intuitive thing. What makes them so hard?
The main point of regexes is that they can use wildcards—symbols which don't match a literal symbol, but any of a (possibly very large set) of (possibly combinations of) literal symbols. (Like using '*' on the command line, but much more powerful and complex.) Using them for any but the simplest tasks thus usually requires a lot abstract, symbolic thought, and generally people aren't too good at being able to follow the combinatorially-explosive number of consequences that can come from changing a single symbol in the regex.

Like, imagine scanning a webpage to find a company's mailing address. As humans, we've got a lot of in-built tolerance for what an "address" might look like—depending on where the company is in the world it might have more or fewer fields than would be the norm in our home country, maybe the street or city name contains multiple separate words, etc. But we have a mental "prototype" of roughly what an address looks like and can use fuzzy logic to recognize things which, while deviating from the strict image of that prototype, are still addresses. Now imagine trying to get a computer to do the same thing; regexes allow you to encapsulate that insane amount of flexibility via (appropriately complex) combinations of wildcards. (Actually attempting to set up a regex that could handle addresses sounds like an unutterable nightmare. )
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