A new web site gives you the chance to improve your regular expressions and have fun at the same time. Regular expression crosswords are like Sudoku for programmers.

If you remember the regular expression crossword set as a part of an MIT Mystery Hunt (if you don't check out Can You Do The Regular Expression Crossword?) then you might have been having withdrawal symptoms once you completed it. Now you can get your fix of regular expression puzzles at a new website that presents you with a graded set and a tutorial just in case you need to brush up on your regular expression grammar. 

Before you get too excited I have to add that none of the regex crosswords come up to the MIT standard. For one thing they are all played on a rectangular rather than a hexagonal grid and they are much smaller - but they are still fun.

The basic idea is that each row and each column in the grid is assigned a regular expression. Each regular expression specifies the pattern of characters allowed in the row and column. Usually the pattern can be satisfied by many choices of characters but the intersections of the rows and columns are controlled by two regular expressions and this limits the choice to just one - the solution to the puzzle.

For example, the very first puzzle (spoiler alert) is:

To play you simply go to the site select the difficulty level and start entering your solutions. If you want the site to keep track of your score you can sign in with your Facebook account. There is a help page that explains some simple regular expressions and a tutorial - after that you are on your own. 

The most difficult of the puzzles has more squares and two regular expressions per row/column:

While the Regex Crossword site is fun you can't help but think that there might be an even more interesting game based on regular expressions trying to get out.