Sorry this is so delayed, but I have to exploit the chance to be anal :-)...
In two of the responses the language of "creating a value" was used, which is also dangerous in a *philosophical* way (I use the term extremely lightly), in such that an "expression" could also *create* NO value (aka undef, or NULL) in which case it is an expression that is creating (for lack of a better english word) a response (though I am sure this isn't precise enough either), even though that response has no value, is undefined or NULL. Though I will give kudos for the one example given earlier: "Also, a regular expression is an expression that fits a range of definitions, but still in it's own polymorphic way is a 'value' and can be tested against other values to see if it is the 'same as' or not." And possibly this is why we call it a new language, or its *own* language, rather than pseudo-enlish-code or something, right drieux?? ;-) http://danconia.org Cody Art Supply LLC wrote: > Hi, > > I'm pretty new to perl, but I think this may help: > > I believe a good 'rule of thumb' test can be "can that 'whole area that I think may >be an expression' be used as having some type of value?" > > The reason '$x = $y + 2' is an expression is because you can legally (although >almost never done on purpose) use that as a value, say in 'if ($x = $y + 2) {}'. The >resulting value that is returned by that expression is the value of $x. (Most of the >time when you see that in an 'if' statement, the coder meant to use the '==' >comparison instead of the '=' assignment.) > > In your question you asked 'for (my $x = 0; $x <= 100; $x++){}' being an expression. > > It contains three expressions, 'my $x = 0', '$x <= 100', and '$x++' but the whole >block isn't one itself. Only the middle one is used as an expression by the >interpreter, because it's value is observed at the beginning of every iteration in >the loop to see if it is equal to 'true'. The first expression is only used to >initialize the start of the loop, and the last expression is used to create a change, >to ensure the loop's condition will vary and eventually test false and exit. > Because of that, although they pass the 'expressions' test, you'd probably call them >'assignment operations' because that is their primary use, which better describes >their use within that context. Still, in that case they are both assignments and >expressions. > > As for 'for (0..100){}', it is a shortcut loop that hides the expressions by >declaring them implicitly... I think. It's not an expression itself. > > Also, a regular expression is an expression that fits a range of definitions, but >still in it's own polymorphic way is a 'value' and can be tested against other values >to see if it is the 'same as' or not. Unlike most expressions, regular expressions >can't be reduced to an actual 'literal' value, in the way (5+4) is reduced to a >literal 9. > > Often, if you are confused if something is an expression or not, you may be looking >at a block of code that contains expressions inside of it, but is not one itself. > > Hope this helps! > > -----Original Message----- > From: Connie Chan [mailto:[EMAIL PROTECTED]] > Sent: Saturday, July 27, 2002 7:15 AM > To: Jenda Krynicky; begin begin > Subject: Re: Syntax Culture > > > > >>These are all expressions: >>1 >>1 + 2 >>$x * 2 >>foo(1,2,3) + 49 >>(1,2) x 2 >>$x == $y >>$x < 5 >>$x > 1 && $x < 5 >>but even this is an expression: >>$x = $y + 2 >> >>Basicaly "expression" is something that creates a value that you can >>assign to a variable, pass to a function or use as a condition. >> >>This means that >>$x = $y + 2 >>IS an expression, but >>$x = $y + 2; >>IS NOT! It's a statement. >> > > > With this, I'll have a question again =) > how about : for (my $x = 0; $x <= 100; $x++){} ? > In every loop, $x return the value to the middle, > and the middle design to roll another loop or not. > It is doing something similar to if then else, but > it also returning vals and condition signals... > So.... what is this ? And when I write as > for (0..100){} there is quite no difference, still > an invisible $x, as $_... so...sorry, dunno how to ask.. =) > > Rgds, > Connie > > > > -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
