[Haskell wikibook] Truth values and a couple other things

[Daniel Mlot]

While trying to think about how I could tackle the section on numerical 
types in "Type basics" I found out that I couldn't reason properly about 
it without knowing to which extent types would be discussed in the 
previous sections. That led me to "jump the gun" and attempt writing the 
bulk of the section myself. Apfelmus, please forgive me if that bothers 
you in any way (for instance, if you had a draft of your own being 
prepared) - in any case, just as I took some liberties with your outline 
feel free to do the same and turn my text upside down if you feel the 
need to :)

I will use this message to register some issues that are roaming in my 
mind lest I forget to mention them:

* Since we are reorganizing and rewriting most of the first chapters 
anyway it could be a good opportunity to standardize the style of code 
blocks. One option would be just using <source> tags everywhere to get 
syntax highlighting (with recent changes to the Wikibooks CSS files 
<source> is also bundled with the standard grey background box). There 
would be a couple possible issues to consider, though. We would probably 
have to do some template engineering, although I don't think that would 
be too troublesome. Another source of annoyance would be that GHCi 
printouts, ubiquitous on the early chapters, wouldn't be subject to the 
same standardization. Finally, there is the didactic concern of whether 
highlighting can be distracting for complete newbies during the first 
few modules (I do not have a really strong position on the subject but 
feel that "plain" plain text does have some charm due to sheer 
simplicity and transparency).

* One thing that occurred to me while writing about guards: is it even 
accurate to speak of our if/else and related constructs as "control 
structures"? Even if it is correct, is there any better term to use - 
one that does not have such imperative undertones?

Regards,
Daniel Mlot