Archive for 15th January 2008

Future values via multi-threading

Future values

A previous post described future values (or simply “futures”), which are values depend on information from the future, e.g., from the real world. There I gave a simple denotational semantics for future values as time/value pairs. This post describes the multi-threaded implementation of futures in Reactive‘s Data.Reactive module.

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Future values

A future value (or simply “future”) is a value that might not be knowable until a later time, such as “the value of the next key you press”, or “the value of LambdaPix stock at noon next Monday” (both from the time you first read this sentence), or “how many tries it will take me to blow out all the candles on my next birthday cake”. Unlike an imperative computation, each future has a unique value — although you probably cannot yet know what that value is. I’ve implemented this notion of futures as part of a library Reactive.


  • 2008-04-04: tweaked tag; removed first section heading.

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Switching blog engines

I gave up on Blogger, where I’d been keeping my technical blog. Blogger was removing one leading space per line of pre-formatted html (“code”) on every edit/preview cycle.

Meanwhile, I’ve been enjoying using Markdown, so I poked aroud and found a WordPress solution I think I’ll like for a while. You’re looking at it.

The steps are described in a post on Syntax highlighting with Markdown in WordPress. It uses a combination of PHP Markdown Extra and GeSHi (Generic Syntax Highlighter), plus a small extension to specify which language for a block of code. It works great. I tweaked the PHP code to make the default language be Haskell instead of txt. The GeSHi-decorated code even has links to library documentation, which I love.

I had a bit of trouble along the way and got help on the #wordpress IRC channel. It turned out that I hadn’t followed the installation directions for PHP Markdown Extra, which say to move markdown.php out of its directory directly into my plugins directory. Once I knew to look in the Apache error log, it was pretty easy to track down the problem.

Still to do:

  • Work out how to automatically add documentation links to GeSHi. For now, I’ve manually added Data.Monoid, Control.Applicative, and Control.Arrow.
  • When I want to go public, get Haskell Planet to point to the new blog.