Twentyseven 1.0.0
Posted on August 1, 2025
Twelve years of Haskell
Twentyseven is a Rubik’s cube solver and one of my earliest projects in Haskell. The first commit dates from January 2014, and version 0.0.0 was uploaded on Hackage in March 2016.
I first heard of Haskell in a course on lambda calculus in 2013. A programming language with lazy evaluation sounded like a crazy idea, so I gave it a try. Since then, I have kept writing in Haskell as my favorite language. For me it is the ideal blend of programming and math. And a Rubik’s cube solver is a great excuse for doing group theory.
Twentyseven 1.0.0 is more of a commemorative release for myself, with the goal of making it compile with the current version of GHC (9.12). There was surprisingly little breakage:
Aside from that, the code is basically just as it was 9 years ago, including design decisions that I would find questionable today. For example, I use unsafePerformIO to read precomputed tables into top-level constants, but the location of the files to read from can be configured by command-line arguments, so I better make sure that the tables are not forced before the location is set…
How Twentyseven works
The input of the program is a string enumerating the 54 facelets of a Rubik’s cube, each character represents one color.
DDDFUDLRB FUFDLLLRR UBLBFDFUD ULBFRULLB RRRLBBRUB UBFFDFDRU
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