instance ArrowLoop SF where
loop (SF f) = SF $ \as ->
let (bs,cs) = unzip (f (zip as (stream cs)))
in bs

And here it is the (more cryptic definition I propose

loop (SF f) = SF $ loop $ second stream >>> uncurry zip >>> f >>> unzip

where I especially like the fact that “loop” of SF functions it is defined in terms of (built-in) looping functions of type ([a],[c]) -> ([b], [c]). In this way you reuse the main idea of looping, which is encoded in Control.Arrow when defining (->) as an instance of ArrowLoop.

>> [1,2,3].zip [4,5,6], [7,8,9,10]
=> [[1, 4, 7], [2, 5, 8], [3, 6, 9]]

Prelude Data.List> transpose [[1,2,3], [4,5,6], [7,8,9,10]]
[[1,4,7],[2,5,8],[3,6,9],[10]]

Het feit dat Haskell goed omgaat met lijsten van verschillende lengte is extreem handig in de situaties waar ik transpose tot nu toe in gebruikt heb.

(1) You’re right, the HTML is invalid too Unfortunately I can only blame WordPress and myself for picking WordPress. We will probably try to move this blog. (I hadn’t noticed it, because Opera renders it as ‘intended’)

(2) Great idea. I choose to use ‘\ignore’ because of a comment on the Haskell wiki, but doing it the lhs2TeX-way seems much more sensible.

(3) I’m only using parts of the code (which can easily be done), but also from different files which I want to present mixed. Also, I want the code to be runnable. Because there’s Template Haskell involved, I can’t put the code together in one file. So, yeah, it’s a pretty rare problem. If there’s another or better way to do it, I’d love to hear it

I have a number of comments though:

(1) The code blocks look wrong in my browser. Only the first line is framed, the rest is formatted like ordinary text in a proportional font.

(2) Instead of a command like \ignore, it’s better to use %if directives on lhs2TeX’s side to exclude stuff. The reason is that a command like \ignore in TeX can still have subtle effects. For example, the way you define \ignore, it can easily lead to extra whitespace being included in your TeX output.

(3) What exactly do you need the construction for that you first define all the frames and then use them? I’ve never needed that in any presentation. I can imagine some situations (where you want to repeat a frame in several situations) where this would be useful, but they’re relatively rare. Am I missing something?

map echo 1 2 ‘3 4′

you get the numbers 1-4 each printed on a separate line, which means the whitespace within the argument ‘3 4′ is lost. If however you make the change I suggested, you get:

1
2
3 4

which is correct.

Also, see the BSD apply(1) command:

NAME
apply — apply a command to a set of arguments

SYNOPSIS
apply [-a c] [-d] [-#] command argument …

DESCRIPTION
The apply utility runs the named command on each argument argument in turn.

It’s available on Mac OS X, if you have that.

The code doesn’t do much, actually. I forgot to tell something about the ‘features’ in the post but some thing it does:

* Minimize the width of timetable by splitting at the biggest ‘gap’ (and not at midnight).
* Calculate all sets of days, sorting them on the number of days.
* The colors of the sets go from dark to light. So, the darker the dot, the more days it accounts for.

@Ben: the reason the dots are gray is mainly that it should be printable on my laser printer