[plt-scheme] DrScheme Can't Insert Negative Fractions?

The dialog (Insert/Insert Fraction... in the DrScheme IDE) is rather 
ambiguous as to what it does: there's no notion of adding or 
subtracting, just three text fields that accept integer input.  "Opens a 
dialog for a mixed-notation fraction, and inserts the given fraction 
into the current editor." per the doc.

(If you enter "foo" "bar" and "mung" in the three fields, or even just 
one, DrScheme presents the error "Invalid number: must be an exact, 
real, non-integral number.")

Carl Eastlund wrote:
> Did you accidentally add 7/9 to -17?  That would give you -16 2/9, as
> you saw.  You need to remember to subtract the 7/9, because it's
> negative too.  Or add -7/9.
>
> On Sun, Aug 31, 2008 at 12:01 PM, Grant Rettke <grettke at acm.org> wrote:
>   
>> This message was originally posted here:
>> http://groups.google.com/group/study-htdp/browse_thread/thread/4be081a64769dcfb
>> by my friend Kartik.
>>
>> DrScheme allows adding fractions via Menu->Special->Insert Fraction.
>> However, when I try inserting a fraction for -17 7/9 it gets converted
>> to -16 2/9.
>>
>> Is this a bug?  17 7/9 by itself gets added properly but not its
>> equivalent negative value.
>>     
> __