# DrScheme Can't Insert Negative Fractions?

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### Kartik

Aug 31, 2008, 10:38:53 AM8/31/08
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While attempting to solve fahrenheit to celsius problem I was trying
to add a simple test which tests the following condition

(= (fahrenheit-to-celsius 0) -17 7/9)

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.

Kartik

### Douglas Gregor

Aug 31, 2008, 1:18:44 PM8/31/08
It is not a bug. -17 7/9 can be reduced to -16 2/9. DrScheme reduced
the fraction.

### Grant Rettke

Aug 31, 2008, 1:48:12 PM8/31/08
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Hi Kartik,

I figured you would prefer a reply when you woke up, so I posted your
post to the PLT group. It turns out that the way the insert fraction
dialog box is like this:

It takes the whole part and adds it to the fraction specified by the
numerator and denominator. So when we enter -17 it adds that to 7/9,
resulting in -16 2/9. You can run this in the Interactions window:

(check-expect (+ -17 (/ 7 9)) (- (+ 16 (/ 2 9))))

So there are two options:

1. Use the insert fraction dialog with this in mind.
2. Type the fraction out manually: (- (+ 17 (/ 7 9)))

Best wishes,

Grant

### Kartik

Aug 31, 2008, 1:54:55 PM8/31/08
Hi Grant,

It makes sense now.

Thanks much Douglas, Grant!

Kartik
--
Stay away from drunk acronym - it is inabbreviated.

### Barry Brown

Aug 31, 2008, 2:07:07 PM8/31/08
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DrScheme does support proper and improper fractions natively. If you
want to type in the fraction 7/9, just type in 7/9. It's equivalent to
(/ 7 9). But it only understands fractions with a numerator and a
denominator. To do -17 7/9, you'd have to write it one of a few ways:

-160/9
(- (+ 17 7/9))
(- -17 7/9)

### Douglas Gregor

Aug 31, 2008, 3:32:12 PM8/31/08
OK. There is a negative sign in front of the mixed fraction. -17 7/9
is the same as writing -17/1 + 7/9 = -146/9. This can be reduced to
-16 2/9. Now, 17 7/9 is the same as writing 17/1 + 7/9 = 160/9 = 17
7/9.

If you're going to use the menu (Insert -> Insert Fraction...),
understand what it's doing. I guess this is getting into more math
then Scheme. There are fractions, improper fractions, and mixed
fractions understand what's happening to them or what you're doing to
them especially when dealing with a negative whole number or a
negative improper fraction.

Below, of course they're not equal. But, -17 7/9 and -16 2/9 can be
reduced. The comparison for equality should use the values -142/9 and
-146/9

(= (/ -142 9) (/ -146 9)) and this is false.

-1 is atomic; therefore, I assume -146 is atomic. -17 is atomic. -17
7/9 isn't atomic because it's an expression. -17/1 + 7/9

(+ (/ -17 1) (/ 7 9))

The kids are screaming... I have to play with them.

### kerrangster

Aug 31, 2008, 9:28:22 PM8/31/08
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I guess it was a bug.

On Aug 31, 2:32 pm, "Douglas Gregor" <kerrangs...@gmail.com> wrote:
> OK.  There is a negative sign in front of the mixed fraction.  -17 7/9
> is the same as writing -17/1 + 7/9 = -146/9.  This can be reduced to
> -16 2/9.  Now, 17 7/9 is the same as writing 17/1 + 7/9 = 160/9 = 17
> 7/9.
>
> If you're going to use the menu (Insert -> Insert Fraction...),
> understand what it's doing.  I guess this is getting into more math
> then Scheme.  There are fractions, improper fractions, and mixed
> fractions understand what's happening to them or what you're doing to
> them especially when dealing with a negative whole number or a
> negative improper fraction.
>
> Below, of course they're not equal.  But, -17 7/9 and -16 2/9 can be
> reduced.  The comparison for equality should use the values -142/9 and
> -146/9
>
> (= (/ -142 9) (/ -146 9)) and this is false.
>
> -1 is atomic; therefore, I assume -146 is atomic.  -17 is atomic.  -17
> 7/9 isn't atomic because it's an expression.  -17/1 + 7/9
>
> (+ (/ -17 1) (/ 7 9))
>
> The kids are screaming... I have to play with them.
>