Weiqi Gao's Observations - gnu tag

Friday C Quiz: Know Your Closures

Fri, 04 Apr 2008 12:11:48 GMT

You know what? This closure thing has gotten into my head. I know it's pointless and useless to think and talk about it all the time, but I can't help it.

Well, my loss is your gain. And today's Friday quiz will take you all the way back to C. Yes, old trusty C! Although ANSI C does not support closures, some C compilers provide nested function extensions that provide a limited subset of closure functionalities such as accessing variables in the outer function.

Q: Will the following C program compile and run under your C compiler? If so, what will it print?


  #include <stdio.h>
  
  int main() {
    int (*pFib)(int);
    int fib(int n) {
      return n == 0 ? 0 :
             n == 1 ? 1 :
             pFib(n - 1) + pFib(n - 2);
    }
    pFib = fib;
    printf("%d\n", pFib(6));
    return 0;
  }

GNU grep's New Trick

Sat, 10 Jun 2006 16:23:48 GMT

I stumbled upon this Linux.com article: GNU grep's new features about a week ago. (No, the StumbleUpon Firefox plugin was not used.) I printed it out but only got a chance reading it on Thursday.

It talked about several new features in GNU grep 2.5 that's pretty neat. I've already used two of the features at work yesterday. But before I go on, let me see a show of hands, how many of you are using GNU grep 2.5? 2.4? 2.0? Right, chances are that you don't know or much care which version of grep you are using. I didn't know until I read the article. (I'm using GNU grep 2.5.1, which is a patch level behind the latest release. Must download, ./configure; make; make check; make install! ...Not! By the way, 2.5 was out in 2002—four years ago.)

The features I used are called --only-matching and --color. The --only-matching feature can also be specified using the -o option on the command line and it shows only the part of a matching line that matches PATTERN. The --color feature will show the matching portion of the line in color (by default red).

I find myself using the --color option to experiment with the regular expressions and then using the -o option to get the matching text for further processing:

[weiqi@gao]$ cat foo
This is a test.
[weiqi@gao]$ grep --color test foo
This is a test.
[weiqi@gao]$ grep -o test foo
test

For more complicated regular expressions, the color option gives a better visual feedback.

Give these new options a try.

GNU's Now Unix

Sat, 11 Feb 2006 00:30:24 GMT

Tim Bray: I think Sun could legally ship something like this under the name “GNU/Unix”. Which would be concise, descriptive, accurate, and funny. (Because GNU stands for “Gnu’s Not Unix” and Solaris, after all, is.)

I was chatting this over with Simon Phipps and he suggested that GNU could stand for “Gnu’s Now Unix”.