I am sure the code above is poetry for those deep into it, but for a person who is a bit rusty (or god forbid, new to the code base), this is basically indecipherable. Look at how many tokens are there in a line like

(each c (dedup (map downcase (trues [uvar _ topcolor] (keys profs*))))

How many people can answer the question of which ones are macros, functions, simple identifiers and so on? In that particular example I am stumped at [uvar _ topcolor] and can't get past it.

Yes, I have read Paul's thesis on Lisp code density (quick summary: each line is dense, but there is a lot less overall code so it evens out or better), but my counter would be that there is a density beyond which most mortal brains can't penetrate.

Without intending to cause offense, I am going to say that this is tending to write-only code. Sure, the equivalent Ruby or Python (leave alone blubs like Java or C#) would be pages long, but I suspect that lower density leads to better understandability.

  (each c (dedup (map downcase (trues [uvar _ topcolor] (keys profs*))))
    (do-stuff-with c))

  keys(profs*).find_all{|prof| uvar(prof, topcolor)}.map(lambda {|str| str.downcase}).uniq.each do |c|
    do_stuff_with(c)
  end

There's not really a concept of lines in Lisp; you can break expressions wherever you like. E.g. you could also write:

  (defop topcolors req
    (minipage "Custom Colors"    
      (tab 
        (each c (dedup (map downcase 
                            (trues [uvar _ topcolor]    
                                   (keys profs*))))
          (tr (td c)
              (tdcolor (hex>color c) 
                (hspace 30)))))))

- You can look ahead easier and get a bird's-eye-view - Once you learn an operator, recognizing it (and writing it correctly) becomes a single word instead of said line/block/idiom.

My guess is that [uvar _ topcolor] is a function similar to (lambda (x) (uvar x topcolor)). That's just a guess, but once I learn whatever it is, I'd wage that it's easier to recognize and debug the bracket syntax.

I doubt it's the density that's the problem. I also doubt macros are. It's more like whether you recognize "the way" in which you're supposed to write, in the given language. Any language, verbose or terse, is indecipherable until you get familiar with the way even you know the syntax and semantics of the language.

My broader point still holds though - there is a maximal density ...

And the reason I commented on it was that in posting that code fragment, the message was that it would be "kind of obvious" to any reasonably competent programmers how macros really help. I agree macros really do help, so no quarrel there.

In this case, we understand the "application" perfectly, and then we get to see the code. It still got (some of us) stumped, and (some of us again) actually know about macros and are moderately familiar with Lisp idioms. That is why I asked if density can go too far.

Compare that to something like LINQ, which I am coincidentally studying. It is a DSL for querying object collections (a similar use case to the code here). With no special background, you can go in, read code, and get a reasonable idea of what is going on.

LINQ actually lets you get rid of a lot of code (something I agree with in general), so it lives much higher on the density scale than a typical blub.

Less code = faster development, easier maintenance, fewer bugs

Ultimately that's the choice of the designer; not all languages need to address to the broad range of programmers.

each = mutant foreach

dedup = remove duplicates

(trues [] (keys profs*)) would mean "map the lambda (predicate) over the list of keys to the hash of profiles, returning a list of elements for which it returned #t."

A few more specifics about the application and language would make this comprehensible.

  (def keep (f seq) (rem [no (f _)] seq))

  (def trues (f seq) (rem nil (map f seq)))

From PG's post above, it seems like those are fairly evenly distributed across macros and functions. I don't need to know whether td is a macro or function to guess that it outputs a table data cell. I do need to know that it outputs a table data cell, and I only know that because I'm familiar with HTML.

Reminds me of mathematical proofs, where you work out everything offline, and then make the proof elegantly brief. There is a similar process going on here - writing macros really does boil down to that kind of offline work.

Just as with such elegant proofs, though, you do need a pencil and paper to trace through the steps. And if the programmer were anything but of the highest caliber, it is fairly easy to get tripped up.

The way blub languages handle (the absence of) macros for td, tr etc. is to invent templating languages (JSP etc) where you embed Java inside HTML. You basically have a DSL living in a separate syntactic space. That gets the job done, for the specific problem space at hand (web apps).

I have come to like that syntactic space separation: HTML lives as HTML, SQL lives as SQL and so on. With macros, you are getting everything to live in the same syntactic space, so you get the proliferation of tokens, without that structural separation that aids in comprehension.

http://news.ycombinator.com/item?id=97830