Giles,
Can you explain what that causes? You say "is prone to accidental
assignment". Sounds like variables erroneously change value when
queried. That's not good. My limited experience is different, that
code has all kinds of unexpected and hidden structure because it was
written by people l
He means typing a single = when you meant to type ==.
In mathematics, a single equals means comparison. The concept of
assignment is derived from that, through something like "the value of x
for which the boolean expression x = is true." In C and
languages derived from it, = means assignment
Ooo. This is one that I can answer.
In most computer language syntax, the statement @X = "Y" assigns the
value "Y" to variable @X.
In some comptuer languages, the *expression* ( @X == "Y" ) compares @X
and "Y" for equality (does @X contain the value Y" ?) and returns a
result of true or false.
Phil,
The best way to answer you may be to refer you to a nice overview of
causation written by my colleague Richard Scheines:
http://www.hss.cmu.edu/philosophy/scheines/causation.pdf
He is a member of Glymour's team. Most of their work deals with
"type-causation" or "causation among variables"
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> Giles suggestion, to reverse the order of the terms, is a good one,
> because it prevents a typo from compiling without error and
> accidentally causing an assignment at run-time, and instead generates
> a compile-time error, pointing out the typo!
yeah that's exactly it. these bugs happen a lot
>> // World's last bug
>> if (red_button_pressed = 1)
>>launch_missile();
>
> I thought that was pretty funny ^_^
.. for all 7 of us who understood it!
-- Owen
Owen Densmore http://backspaces.net
FRIAM Applied Complexity
*** tomorrow immediately following Kim Sorvig's 10:30a talk ***
** NOTE location of James Little Theatre **
SPEAKER:
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TITLE:
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TIME: Thurs Oct 26, 11:30a-12:30p
LOCATION:
I was about to say: can someone translate this joke into English? (It
looks funny, but...)
- Original Message -
From: "Owen Densmore" <[EMAIL PROTECTED]>
To: "The Friday Morning Applied Complexity Coffee Group"
Sent: Wednesday, October 25, 2006 8:11 PM
Subject: Re: [FRIAM] div. zero b
In some languages, the assignment operator, "=", not only assigns a
value to a variable, it also returns that value as the expression's
value itself. This is to allow things like
a=b=c=42;
So in the expression
red_button_pressed = 1
The value 1 is assigned to the variable red_b
Easy.Correct version: // World's last bug if (red_button_pressed == 1) launch_missile();The other version is guaranteed to bomb...
-- Doug Roberts, RTI International[EMAIL PROTECTED][EMAIL PROTECTED]505-455-7333 - Office505-670-8195 - Cell
On 10/25/06, David Breecker <[EMAIL PROTECTED]> wrote:
I
Owen Densmore wrote:
> So the *extremely* common bug
> of using = rather than == causes entirely unexpected consequences ..
> launching a missile.
>
I expect to see both in many circumstances.
For example, when opening a file to read that is absent or to write, and
write permission is forbi
> >> // World's last bug
> >> if (red_button_pressed = 1)
> >>launch_missile();
> >
> > I thought that was pretty funny ^_^
>
> .. for all 7 of us who understood it!
>
> -- Owen
The odd thing is it made me laugh a lot, as if I understood the joke,
even though I have no idea what it mea
OK, thanks Doug and Owen, I'm
laughing.
And I'm also noting that Cormac McCarthy
(who has been hanging out at SFI lately, and even thanked the Institute in his
last book) has a new one about a post-nuclear-apocalyptic society ("The
Road"). Could this be the result of programming error?
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