Ron Garret  <rNOSPAMon@flownet.com> wrote:
+---------------
| Frode Vatvedt Fjeld <frodef@cs.uit.no> wrote:
| > Ron Garret <rNOSPAMon@flownet.com> writes:
| > > Because people get confused when they see $199/50 instead of $3.98.
| > 
| > But isn't the presentation of something is separate from its internal
| > representation? If you present something using format and ~$, as would
| > be natural for dollar amounts, it doesn't matter if the representation
| > is float or rational. (format t "~$" 199/50) prints 3.98.
| 
| Yes, I didn't know about the ~$ format directive.
| I'm still pondering the ramifications of allowing e.g. 1/3 of a dollar.
+---------------

The precision of ~$ only *defaults* to 2; you can specify another:

    (format nil "~$" 8/3)     ==> "2.67"
    (format nil "~1$" 8/3)    ==> "2.7"
    (format nil "~4$" 8/3)    ==> "2.6667"

Small "gotcha" to watch for: The ~$ format will [or, is allowed to]
coerce rationals to *single* floats, e.g.:

    (format nil "~20$" 8/3)   ==> "2.66666670000000000000"
    (format nil "~20$" (coerce 8/3 'double-float))
			      ==> "2.66666666666666650000"


-Rob

-----
Rob Warnock			<rpw3@rpw3.org>
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