I assure you there will be no further allusions to Korean earworms. That said, on to the subject at hand...
Remember the exercise in the online Haskell course that had several tests to filter out weak passwords, all of which had to pass for the fictitious system to allow a String value to be used as a password? I wanted to make it easy to change, so I wanted to take a [String -> Bool] and get a [Bool] I could apply and to for the final thumbs up/thumbs down decision.
The first step: roll my own, which has a pleasing symmetry with map if you write it as a list comprehension:
If I don't already have the Haskell subreddit link over on the right, I'll add it ASAP.
This evening a Haskell beginner posted about some trouble he was having writing code to generate a particular sequence. I didn't catch on to the sequence he was going for, but I should have from a comment in his code:
Someone did catch on, though, and asked "Are you trying to make a look and say sequence?" The poster said yes... and off to Wikipedia I went.
Said sequence starts 1, 11, 21, 1211, 111221, ... and the way you get the next term is to take the current one and sort of run-length encode it. The first term would be "one one", i.e. a run of ones of length one, so the second term is 11. That in turn would be described as "two ones", hence the third term is 21, or "one two, one one", giving 1211, and so on.
If each digit were on its own line, you could get the next term of …
I've upgraded to Ubuntu 16.04 beta 2, and so far, as I've read elsewhere, it's working very nicely.
(One warning: if you have apcupsd installed, turn it off before upgrading! During the upgrade, something happens that causes the UPS battery to look fully discharged, and apcupsd will obligingly shut your system down... in mid-upgrade. Others have seen this when upgrading to 15.10.)
Now I'm reinstalling the various packages I had previously installed, but for FP Complete's Haskell Tool Stack, trying the Ubuntu instructions FP Complete gives (mutatis mutandis for the version) doesn't work, at least as I write. It looks like it's made its way into the Ubuntu repositories, so that sudo apt-get install haskell-stack will do the trick. I'm also quite pleased to see that 16.04 is actually up to date with respect to GHC. ghc --version shows it has 7.10.3. (Now to look to see whether it's up to snuff on the libghc* packages in the repositories...)