From: Tanaka Akira <akr@...17n.org>
Date: 2002-01-14T20:09:31+09:00
Subject: Re: MetaRuby : RubySchema.rb howto?

In article <Pine.GSO.4.21.0201141134040.24823-100000@godzilla.ce.chalmers.se>,
  Robert Feldt <feldt@ce.chalmers.se> writes:

> Ok, then there are some simplifications because the standard funcprog
> pretty-printing libraries are known to have non-linear complexities.

Since Wadler's pretty printing is very simple, I think it is possible.
(I think it is simplest.)

> Olaf Chitil:
> Pretty Printing with Lazy Dequeues
> Preliminary Proceedings of the 2001 ACM SIGPLAN Haskell Workshop, Firenze,
> Italy, Universiteit Utrecht UU-CS-2001-23, 2 September 2001, pp. 183-201.
> 
> which is an implementation of Oppen's pretty printing algorithm in
> Haskell. Oppens alg is based on dynamic programming and is fast. I don't
> think it is as expressive as Azero's approach though.

Interesting.

>   you could then get
> 
>     [1, 2, 3, 4,
>      5, 6, 7]
> 
>   which I think is a bit nicer.
> 
> Would it be possible?

Impossible, I think.

> BTW, do you support indented groups like the one for the elements above
> that indent the position of the first element of the second line (5) to
> the same as the first element of the group on the first line (1)?

With prettyprint.rb which is implementation of Wadler's pretty
printing without extentions, I think only two format is possible:

  [1, 2, 3, 4, 5, 6, 7]

or

  [1,
   2,
   3,
   4,
   5,
   6,
   7]

Because breakable positions contained by a (non-nested) group cannot
mix spaces and breaks.

I think we needs more powerful library.  Although I don't know which
algorithm is better: extention to Wadler's or other algorithms.
-- 
Tanaka Akira