Collectables on Go monk

spinner

Wed, 28 Oct 2015 00:00:00 +0000

One go statement keeps a terminal spinner turning while main grinds through a slow computation. Nobody stops the spinner; when main returns, the program ends and takes it along.

func main() {
	go spinner(100 * time.Millisecond)
	const n = 45
	fibN := fib(n) // slow
	fmt.Printf("\rfib(%d) = %d\n", n, fibN)
}

func spinner(delay time.Duration) {
	for {
		for _, r := range `-\|/` {
			fmt.Printf("\r%c", r)
			time.Sleep(delay)
		}
	}
}

func fib(x int) int {
	if x < 2 {
		return x
	}
	return fib(x-1) + fib(x-2)
}

Source: gopl.io/ch8/spinner from The Go Programming Language by Alan Donovan and Brian Kernighan.

A regular expression matcher

Thu, 01 Jan 1998 00:00:00 +0000

Thirty lines of C that match a small but useful subset of regular expressions: c (literal characters), . (any character), ^ and $ (start and end of the text) and * (zero or more of the previous character). Rob Pike wrote them in an hour or two for The Practice of Programming; three small functions, and the recursion does all the work.

Brian Kernighan, his co-author, picked it as his example of beautiful code:

rename

Mon, 30 Jul 1990 00:00:00 +0000

Larry Wall’s bulk file renamer. The renaming rule is not an option or a pattern language; it is any Perl expression that edits $_, so rename 's/\.bak$//' *.bak and rename 'y/A-Z/a-z/' * both just work.

#!/usr/bin/perl
($op = shift) || die "Usage: rename perlexpr [filenames]\n";
if (!@ARGV) {
 @ARGV = <STDIN>;
 chop(@ARGV);
}
for (@ARGV) {
 $was = $_;
 eval $op;
 die $@ if $@;
 rename($was,$_) unless $was eq $_;
}

Source: eg/rename in the Perl distribution.

Designing an authentication system

Mon, 01 Feb 1988 00:00:00 +0000

Not code, but a design. Two developers argue their way to Kerberos one objection at a time: every scene opens with a hole in the previous scene’s scheme and closes with the fix. By the end you know not just how tickets and authenticators work but why each piece has to be there.

Dramatis Personae

Athena an up and coming system developer.
Euripides a seasoned developer and resident crank.

Scene I

Advice on writing

Mon, 14 Dec 1959 00:00:00 +0000

Eight rules C. S. Lewis sent to an American schoolgirl who had written, at her teacher’s suggestion, to ask how to write. Swap the radio and the typewriter for their modern equivalents and nothing here has aged; rule 5 applies to code as much as to prose.

Source: Letters of C. S. Lewis, edited by W. H. Lewis (letter of 14 December 1959).