On Nov 18, 12:03 pm, Chouser <[EMAIL PROTECTED]> wrote:
> On Tue, Nov 18, 2008 at 11:29 AM, [EMAIL PROTECTED]
>
> <[EMAIL PROTECTED]> wrote:
>
> > I looked at Wadler's "A Prettier Printer" paper (http://
> > homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf) and did a
> > rote translation of it into Clojure. Then I wrote printing routines
> > for sequences and maps -- very barebones. They work OK:
>
> I started working on a pretty-printer as well. I wouldn't show it to
> anybody yet, but I also don't want any unnecessary duplicated effort.
> So I'll go ahead and show what I've got so far, and then we can decide
> how to proceed. I have no interest in pursuing my solution if it's not
> a good approach, or if anyone else would rather pursue it.
>
> That is, I want to use a pretty printer, not necessarily write one. :-)
I feel the same way, mostly.
I'm very new to Clojure and not all that experienced in Lisp or
functional programming in general. That's why I started with a port of
an existing skeletal implementation. I think the main advantage of
Wadler's approach -- not to be confused with my port, which I am sure
is in need of fixing-- is that it is bounded -- i.e. the decision to
print horizontally or vertically is made after looking ahead W
characters (W being the line width).
Your implementation needs to get the whole value of pr-str before
deciding that it is too long to put on a single line. But then, your
implementation actually works and doesn't run out of stack space on
short lists. :-)
On that topic, my pp function makes no sense -- it should use doseq to
take advantage of the laziness.
(defn pp
([obj width]
(doseq char (pretty width (show obj))
(print char)))
([obj]
(pp obj 80)))
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