What happens when I evaluate the call the second time?

What happens when I evaluate the call the second time?

[Eric Lilja]

Hello, I've just started with lisp programming and I encountered 
something I thought was odd.

Using GNU Emacs 22.0.990.1 (i386-mingw-nt5.1.2600) of 2007-06-02 on 
MINDCOOLER

Starting with -Q

In the scratch buffer I write

(defun average (x y)
   (/ (+ x y) 2)
)

(average 2 3)

First C-x C-e after the function, then twice after calling it. The 
output is:
average
2
2 (#o2, #x2, ?\C-b)

Now what's the (#o2, #x2, ?\C-b) stuff?

- Eric

PS. I notice that the output is 2 and not 2.5, I guess the output gets 
truncated to an integer (the decimal part is discarded).

Re: What happens when I evaluate the call the second time?

[Mathias Dahl]

> First C-x C-e after the function, then twice after calling it. The
> output is:
> average
> 2
> 2 (#o2, #x2, ?\C-b)
>
> Now what's the (#o2, #x2, ?\C-b) stuff?

Different ways to express 2 I think. What I find strange however, is
that it is only displayed at the second invocation of C-x C-e. If you
for example move point left and right and evaluate again, you first
get 2, then the above.

> PS. I notice that the output is 2 and not 2.5, I guess the output gets
> truncated to an integer (the decimal part is discarded).

Yes. Try with (average 2.0 3) and you will get 2.5.

Re: What happens when I evaluate the call the second time?

[Andreas Schwab]

"Mathias Dahl" <mathias.dahl@gmail.com> writes:

>> First C-x C-e after the function, then twice after calling it. The
>> output is:
>> average
>> 2
>> 2 (#o2, #x2, ?\C-b)
>>
>> Now what's the (#o2, #x2, ?\C-b) stuff?
>
> Different ways to express 2 I think. What I find strange however, is
> that it is only displayed at the second invocation of C-x C-e. 

It's a feature, see eval-expression-print-format.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: What happens when I evaluate the call the second time?

[Lennart Borgman (gmail)]

Andreas Schwab wrote:
> "Mathias Dahl" <mathias.dahl@gmail.com> writes:
> 
>>> First C-x C-e after the function, then twice after calling it. The
>>> output is:
>>> average
>>> 2
>>> 2 (#o2, #x2, ?\C-b)
>>>
>>> Now what's the (#o2, #x2, ?\C-b) stuff?
>> Different ways to express 2 I think. What I find strange however, is
>> that it is only displayed at the second invocation of C-x C-e. 
> 
> It's a feature, see eval-expression-print-format.

I think the thing Erik is asking about is why the output is different in 
the second evaluation.

Re: What happens when I evaluate the call the second time?

[Andreas Schwab]

"Lennart Borgman (gmail)" <lennart.borgman@gmail.com> writes:

> Andreas Schwab wrote:
>> "Mathias Dahl" <mathias.dahl@gmail.com> writes:
>>
>>>> First C-x C-e after the function, then twice after calling it. The
>>>> output is:
>>>> average
>>>> 2
>>>> 2 (#o2, #x2, ?\C-b)
>>>>
>>>> Now what's the (#o2, #x2, ?\C-b) stuff?
>>> Different ways to express 2 I think. What I find strange however, is
>>> that it is only displayed at the second invocation of C-x C-e. 
>>
>> It's a feature, see eval-expression-print-format.
>
> I think the thing Erik is asking about is why the output is different in
> the second evaluation.

That's the feature.  You get the verbose output with the second try.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: What happens when I evaluate the call the second time?

[Lennart Borgman (gmail)]

Andreas Schwab wrote:
> "Lennart Borgman (gmail)" <lennart.borgman@gmail.com> writes:
> 
>> Andreas Schwab wrote:
>>> "Mathias Dahl" <mathias.dahl@gmail.com> writes:
>>>
>>>>> First C-x C-e after the function, then twice after calling it. The
>>>>> output is:
>>>>> average
>>>>> 2
>>>>> 2 (#o2, #x2, ?\C-b)
>>>>>
>>>>> Now what's the (#o2, #x2, ?\C-b) stuff?
>>>> Different ways to express 2 I think. What I find strange however, is
>>>> that it is only displayed at the second invocation of C-x C-e. 
>>> It's a feature, see eval-expression-print-format.
>> I think the thing Erik is asking about is why the output is different in
>> the second evaluation.
> 
> That's the feature.  You get the verbose output with the second try.

Thanks, I see. But eval-expression-print-format does not tell about this 
AFAICS, or?