Adventures in Computer Programming – bakert@gmail.com
I’ve added the most-requested feature to my Fixtures Generator.
You can now enter a newline-delimited list of team names in the initial form and get back team names in the fixture list.
Please let me know if you use it, especially if you have any problems with it.
A formatting function to go from numbers like 333999333.33 to “333,999,999.33” in Haskell. Copes with negative numbers and rounds to 2 dp (easy to add a paramater for that should you wish).
Examples:
*Main> formatDecimal 44 "44.00" *Main> formatDecimal 94280943.4324 "94,280,943.43" *Main> formatDecimal (-89438.329) "-89,438.33"
import Data.Graph.Inductive.Query.Monad (mapFst)
import List
import Text.Printf
formatDecimal d
| d < 0.0 = "-" ++ (formatPositiveDecimal (-d))
| otherwise = formatPositiveDecimal d
where formatPositiveDecimal = uncurry (++) . mapFst addCommas . span (/= '.') . printf "%0.2f"
addCommas = reverse . concat . intersperse "," . unfoldr splitIntoBlocksOfThree . reverse
splitIntoBlocksOfThree l = case splitAt 3 l of ([], _) -> Nothing; p-> Just p
If you know a simpler way or spot anything that should be done differently, please add a comment.
After investigating a lot of blind alleys I think I’ve solved a problem with pushing and pulling to and from a remote repository being very slow. darcs was issuing hundreds of scp commands just to push up a one line change. This seemed to be related to the _darcs/inventory file being a couple of thousand lines long (should be much smaller) on the remote repo.
In the final analysis my advice is very simple:
darcs tagdarcs optimize --reorder-patches command (the reorder patches part may be unnecessary and cause it to be much slower, but it worked for me although it took three hours).This reduced push/pull time from 3 minutes to nearer 3 seconds.
After reading A World of Endless Advertisements I thought it would be interesting to see the AdBlock Plus version next to the unblocked version.
How “ad-supported content” is supported without ads, I don’t know. But as Banksy says:
“Any advertisement in public space that gives you no choice whether you see it or not is yours. It belongs to you. It’s yours to take, re-arrange and re-use. Asking for permission is like asking to keep a rock someone just threw at your head.”
(Faintly amusingly I actually had difficulty writing this post because AdBlock blocked the images I was using because their name contained the word “ads”.)
I had to integrate a haskell program into an existing make-based intrastructure this week. After a few false starts I managed to proxy to cabal through make with the following Makefile. I also added a feature to copy the binary created to a “bin” folder at the same level as the src folder. I’ve used the Haq example name from How to Write a Haskell Program and my cabal setup is similar to the one described there. Trying to compile Setup.lhs or anything more complicated is a mistake and I am assured that runhaskell is portable.
all: runhaskell Setup.lhs configure runhaskell Setup.lhs build cp dist/build/haq/haq ../bin/ clean: runhaskell Setup.lhs clean rm -rf ../bin/*
Haskell seems to be missing a String replace function. Text.Regex.subRegex seemed like overkill. So I wrote one. It actually works on any list, not just Strings.
replace :: Eq a => [a] -> [a] -> [a] -> [a]
replace [] _ _ = []
replace s find repl =
if take (length find) s == find
then repl ++ (replace (drop (length find) s) find repl)
else [head s] ++ (replace (tail s) find repl)
Some examples:
*Main> replace "hello" "h" "" "ello" *Main> replace "hello" "l" "" "heo" *Main> replace "hello" "x" "" "hello" *Main> replace "100,000,000" "," "hello" "100hello000hello000" *Main> replace "100,000,000" "," "" "100000000" *Main> replace [1,2,3] [1] [9] [9,2,3] *Main> replace [4,5,6,1,2,3,7,8,9,2,3,6,5,4,1,2,3] [1,2,3] [10] [4,5,6,10,7,8,9,2,3,6,5,4,10]
If this function is already in the standard libraries somewhere or if this can be improved in some way please leave a comment to let me know. Thanks!
A cautionary tale about installing debian-unstable packages under Ubuntu Dapper.
I needed version 6.6 of the Glasgow Haskell Compiler and Dapper/Edgy only supply version 6.4.2. I found a mailing list post explaining that 6.6 was available under debian-unstable, which is what Ubuntu is based on. So I downloaded the .deb and tried to install it.
No dice. Requires a partcular version of libc6. So go grab that (BIG mistake – this is possibly the most central library in the whole system and switching versions of it was never going to be a good idea). Try to install, find a dependency (tzinfo), try to install the dependency and kapow – failed in mid-install! Tried to overwrite a file that dpkg thought belonged to the locales package.
Now, whatever I did I got something like this:
sudo apt-get -f install Reading package lists... Done Building dependency tree... Done Correcting dependencies... failed. The following packages have unmet dependencies. libc6: Depends: tzdata but it is not installable libc6-dev: Depends: libc6 (= 2.3.6-0ubuntu20) but 2.3.6.ds1-10 is installed libc6-i686: PreDepends: libc6 (= 2.3.6-0ubuntu20) but 2.3.6.ds1-10 is installed E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages. E: Unable to correct dependencies
I tried every combination of: apt-get remove, apt-get install, dpkg -r and dpkg -i with each package name and variations on the package names as well as bare apt-get install -f and using –force and –purge and goodness knows what else (many thanks to the denizens of #ubuntu on freenode for their many suggestions). Whatever I did the system would just tell me it was queueing up to install the debian versions of ghc and libc6 and that it couldn’t work it’s way out of the dependency pickle.
Finally a knight in shining armour by the unexpected name of “crot” came up with this baby:
sudo apt-get install -f libc6/dapper
The /dapper forces the system to install the correct version even though the debian package is also called libc6. Thanks crot!
I leave this blog post for those who try something equally foolish. If you use a package from the wrong distribution or wrong version, this may help you out.
Forget about Vista/Aero, just look at the visual abuses that are possible in the Ubuntu with AIGLX (coming as standard in Feisty in April 2007). Mostly pointless but tremendous fun.
(Mark Shuttleworth calls providing this kind of facility one of the challenges we need to overcome. He hopes to see usability/productivity enhancements as well as pretty bubbles and lines of fire. I hope so too.)
The operator for modular arithmetic in Erlang is rem (for remainder). Took me a while to find that one.
Should you limit the width of your source code? You can’t read code
that goes off the edge of your screen. So your font size, resolution
and monitor all combine to produce a point at which you must break (or
at least wrap) your lines of code.
I don’t like wrapping. Lines of arbitrary length that wrap wherever
I happen to have positioned the right-hand side of my window seem
messy.
Even if you have plenty of room for more columns, standardising on a smaller number means that when reviewing code
you can see changes side by side using a difference viewer.
Given that I am going to insert a line break somewhere in my code,
where should it go?
There are many possible answers.
COBOL allows approximately 66 characters for code (72 columns – space
for line numbers).
Fortran has 72 usable columns from a maximum of 80.
xterm and gnome-terminal (among others) open 80 columns wide by
default. So does emacs.
vim allows 8 columns for line numbers, leaving 72 usable columns on
a standard terminal.
80 columns was built in to Apple //e motherboard.
Sun’s Code Conventions for the Java Programming Language say:
4.1 Line Length
Avoid lines longer than 80 characters, since they’re not handled well by many terminals and tools.
Note: Examples for use in documentation should have a shorter line length-generally no more than 70 characters.
The linux kernel seems to mostly be broken at 80 columns but there are plenty of exceptions (91-column example):
File: linux/drivers/firmware/efivars.c Line: 749
printk(KERN_ERR "efivars: Sysfs attribute export failed with error %d. ", error);
Some people definitely go wider than 80 columns.
If you want to be able to “> ” quote in an email on an 80-column terminal without wrapping, you’ll have to limit yourself to 78, or less for nested quoting.
GNUStep coding standards say 80 columns. So do other standards (cites printing as the reason, not screen space).
72 and 80 seem to have originated with punch cards, but are by far the most common standard. So, is 72 or 80 columns old-fashioned? Pointlessly restrictive? Or is it the One True Way? Make a comment and let me know what you think!