From: Tamas Papp
Subject: iter and finding inside desctructuring-bind
Date: Sat, 21 Jul 2007 14:28:21 +0000
Message-ID: <878x99q1a2.fsf@pu100877.student.princeton.edu>

Hi,

I have a list of numbers, and I want to calculate all their extents
and find the widest (using a function called text-extents, which
returns four values).

I tried it like this:

(defun measure-axis-numbers (axis-numbers)
  (iter
    (for x in axis-numbers)
    (multiple-value-bind (x-bearing y-bearing width height)
	(text-extents x)
      (collect (list x x-bearing y-bearing width height))
      (finding width maximizing width))))

There is a problem in the last part with finding, how can I make it
work?

Thanks,

Tamas

From: Pillsy
Subject: Re: iter and finding inside desctructuring-bind
Date: Sat, 21 Jul 2007 16:54:55 +0000
Message-ID: <1185036895.185237.245800@n60g2000hse.googlegroups.com>

Tamas Papp wrote:
[...]
> I tried it like this:

> (defun measure-axis-numbers (axis-numbers)
>   (iter
>     (for x in axis-numbers)
>     (multiple-value-bind (x-bearing y-bearing width height)
> 	(text-extents x)
>       (collect (list x x-bearing y-bearing width height))
>       (finding width maximizing width))))

> There is a problem in the last part with finding, how can I make it
> work?

You're trying to do two things and obtain two values, but as written,
the ITER form only returns one value and only sets up a single binding
for the results of both the COLLECT and FINDING clauses. Use :INTO
with each, and then do (finally (return (values ...))).

Also, you can do VALUES destructuring with FOR clauses, like this:

(for (values x-bearing y-bearing width height) := (text-extents x))

It's a little terser and looks more pleasingly ITERATEy.

Cheers,
Pillsy