Clipping Output

[ELIOT%cs.umass.edu@RELAY.CS.NET]

Is there any good way, preferably in FORMAT to
clip output longer than a specified length?

I am using FORMAT to create a string from
a list, but I only want the first 10 or 20 characters.

The effect I need is equivalent to:

(subseq (format nil "~a" XXX) 0 20))

but I would rather not do all the consing that
this implies.

In general, I would like to be able to specify
the maximum field width of most of the format
directives.