Nice line from Erik Meijer via Twitter:
Happiness is when you drill a tunnel from two completely different sides (theory <–> practice) and then they line up *exactly*.
Month: February 2014
Where combinator names come from
Today I found out where the one-letter names of some functions in combinatory logic come from. I’d seen these before (for example, in To Mock a Mockingbird) but I had no idea what inspired the names.
These functions — I, K, S, T, and Z — are known as the Schönfinkel combinators, and their names are somewhat mnemonic in German. (Only somewhat. Don’t get your hopes up.)
| Definition | Name | Name origin |
| λx. x | I | Identitätsfunktion (identity function) |
| λx,y. x | K | Konstanzfunktion (constant function) |
| λx,y,z. xz(yz) | S | Verschmelzungsfunktion (amalgamation function) |
| λx,y,z. xzy | T | Vertauschungsfunktion (exchange function) |
| λx,y,z. x(yz) | Z | Zusammensetzungsfunktion (composition function) |
Source: Practical Foundations of Mathematics, footnote on page 89. Available online here.
What good is an old weather forecast?
Why would anyone care about what the weather was predicted to be once you know what the weather actually was? Because people make decisions based in part on weather predictions, not just weather. Eric Floehr of ForecastWatch told me that people are starting to realize this and are increasingly interested in his historical prediction data.
This morning I thought about what Eric said when I saw a little snow. Last Tuesday was predicted to see ice and schools all over the Houston area closed. As it turned out, there was only a tiny amount of ice and the streets were clear. This morning there actually is snow and ice in the area, though not much, and the schools are all open. (There’s snow out in Cypress where I live, but I don’t think there is in Houston proper.)
Aftermath of last Tuesday’s storm
Related posts
Math diagrams
Time and Productivity
Contractors were working on my house all last week. I needed to be home to let them in, to answer questions, etc., but the noise and interruptions meant that home wasn’t a good place for me to work. In addition, my Internet connection was out for most of the week and I had a hard disk failure.
Looking back on the week, my first thought was that the week had been an almost total loss, neither productive nor relaxing. But that’s not right. The work I did do made a difference, reinforcing my belief that effort and results are only weakly correlated. (See Weinberg’s law of twins.)
Sometimes you have a burst of insight or creativity, accomplishing more in a few minutes than in an ordinary day. But that didn’t happen last week.
Sometimes your efforts are unusually successful, either because of the preparation of previous work or for unknown reasons. That did happen last week.
Sometimes you simply work on more important tasks out of necessity. Having less time to work gives focus and keeps work from expanding to fill the time allowed. That also happened last week.
* * *
I did get out of the house last Tuesday and wrote about it in my previous post on quality over quantity. This turned out to the theme of the week.