Thanks Gil, that helped me to understand the context of the code presented
in the book.
Le 18 sept. 2016 18:02, "Gil Magno" <gilma...@gilmagno.com> a écrit :
> Hi Khalil
>
> 'say' creates list context. So if 'say' receives the list ('one', 'cd',
> 'qw') it will print 'abcdqw'.
>
> 'reverse' creates list context. So if 'reverse' receives the list ('ab',
> 'cd', 'qw') it will return a list with the same elements, but with its
> order inverted ('qw', 'bc', 'ab').
>
> The catch is that if 'reverse' is forced to be evaluated in scalar
> context, then it will 1) concatenate the elements of the list we give to
> it, 2) treat the concatenated result as a string and 3) invert the string.
>
> To force one expression to be evaluated in scalar context, you should
> give that expression as an argument to the 'scalar' function. So in
> reverse(1, 2, 3); 'reverse' is evaluated in *list* context and the list
> returned is (3, 2, 1) , but in scalar(reverse(1, 2, 3)) 'reverse' is
> evaluated in *scalar* context, so 1, 2, 3 are concatenated to the string
> '123', then the string is inverted to '321' and then it is returned by
> 'reverse'.
>
> Now we come to 'say'. 'say' still creates list context, but the list it
> receives from scalar(reverse(1, 2, 3)) is a list of just one element:
> the element '321'. So 'say' prints '321'.
>
> If you didn't understand something or if it is still confuse, don't
> hesitate to ask further questions. :)
>
> On 18/09/16 12:43, khalil zakaria Zemmoura wrote:
> > Hi everyone,
> >
> > I'm reading the modern perl book and I have some questions to address
> about
> > scalar and list context.
> >
> > Here is the code that I want to understand.
> >
> > while (<>) { chomp; say scalar reverse; }
> >
> > Where I'm struggling is : say scalar reverse;
> >
> > The book says that 'say' impose list context to Its operands. 'reverse'
> > impose list context on to its operands and treat them as a list in list
> > context and a concatenated string in scalar context.
> >
> > The questions are:
> >
> > Is 'say' that is imposing list context in 'reverse' or 'reverse' it self
> > treats it's operands in list context or it's both?
> >
> > The most confusing part:
> > There is 'scalar' before 'reverse', so 'reverse' is evaluated in scalar
> > context!
> > So how can reverse executing in both contexts (list and scalar context)?
> >
> > I'm sure I missed something.
> >
> > It will be great if I have more explanation.
> >
> > Thank you.
> > Regards, Zakaria
> >
>
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