Hugh Winkler holding forth on computing and the Web

Saturday, May 27, 2006

Peter Seibel Video

Peter Seibel, author of the excellent Practical Common Lisp, gave this hour long presentation at Google, evangelizing Common Lisp. And here are the top three reasons CL rules and Java sort of sucks:

3. He gives a good worked example of using CL generics to replace miles of Java code implementing the visitor pattern. The key is the "double dispatching" in the pattern: You visit each node, calling some polymorphic method; you pass the method a reference to the calling object, which may itself be polymorphic. So the number of cases to dispatch is m * n, where m and n are the number of possible types for each of the two objects involved in the call. In CL, you just create a generic with m * n implementations; in Java, well, you have to touch a lot more code.

2. He contrasts ordinary try/catch exception handling with CL's conditions mechanism. Java unwinds the stack, losing all the state; CL notifies handlers up the stack without yet unwinding the stack, so that a handler up the stack can ask a function lower down to restart.

1. CL Macros let you abstract out syntax paterns.

It's the kind of video you can mostly listen to and only watch occasionally, as you get other work done -- just the way you'd do if you were at the presentation.

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