[Moscow.pm] Особенности парсера?

[Vladimir Timofeev]

2012/10/31 Maxim Vuets <maxim.vuets на gmail.com>:
> On Wed, Oct 31, 2012 at 12:07:54AM +0400, Vladimir Timofeev wrote:
>>perl -e '@A=(1..10); %B=map { "$_"=>1 } @A;'
>
> perl -e '@A=(1..10); %B=map { "$_"=>1 }, @A;'
>
> Только делает оно не то, что ожидалось.
>
>>Первый из них выдает syntax error
>>Вопрос, почему?
>
> Компилятор подсказывает:
>     Array found where operator expected at -e line 1, near "} "
>         (Missing operator before  ?)
>         Not enough arguments for map at -e line 1, near "} @A"
>
> map имеет две формы:
>
>     map BLOCK LIST
>     map EXPR,LIST
>
> Там же в документации есть большой пример и объяснение:
>
>     "{" starts both hash references and blocks, so "map { ..." could be either the
>     start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look ahead for
>     the closing "}" it has to take a guess at which it's dealing with based on what
>     it finds just after the "{". Usually it gets it right, but if it doesn't it
>     won't realize something is wrong until it gets to the "}" and encounters the
>     missing (or unexpected) comma. The syntax error will be reported close to the
>     "}", but you'll need to change something near the "{" such as using a unary "+"
>     to give Perl some help:
>
>        %hash = map {  "\L$_" => 1  } @array  # perl guesses EXPR.  wrong
>        %hash = map { +"\L$_" => 1  } @array  # perl guesses BLOCK. right
>        %hash = map { ("\L$_" => 1) } @array  # this also works
>        %hash = map {  lc($_) => 1  } @array  # as does this.
>        %hash = map +( lc($_) => 1 ), @array  # this is EXPR and works!
>
>        %hash = map  ( lc($_), 1 ),   @array  # evaluates to (1, @array)
>
>     or to force an anon hash constructor use "+{":
>
>        @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs comma at end
>
>     to get a list of anonymous hashes each with only one entry apiece.
>
> Компилятору показалось, что это EXPR, потому он ожидал запятую.

Мдя... в эти доки я уже пару лет как не заглядывал, сенкс...
Но все равно забавно ;-)

-- 
Vladimir Timofeev <vovkasm на gmail.com>