How do I call sort with an anonymous subroutine stored in a hash ??
 

Hi, I haven't being using perl for too long. Can someone explain the
correct way to get the sort function to recognize an anonymous function
declared as a hash value? Look at my sample code for clarification:

#!/usr/bin/perl

@my_array = qw( g a z f u q m i e b );
$hash{my_sort_sub} = sub { $a cmp $b };
$hash{test_routine} = sub { print "test_routine works\n" };
&{$hash{test_routine}};
print @my_array;
print "\n";
print( sort &{$hash{my_sort_sub}} @my_array );
print "\n";


The code fails to compile with error:

Array found where operator expected at ./test.pl line 9, near "} "
(Missing operator before ?)
syntax error at ./test.pl line 9, near "} @my_array "
Execution of ./test.pl aborted due to compilation errors.

Help! I don't see what's wrong with this.

Re: How do I call sort with an anonymous subroutine stored in a hash ??
 

Casey <mail@nowhere.com> wrote in message news:<pan.2004.01.30.07.28.21.56357@nowhere.com>.. .
> Can someone explain the
> correct way to get the sort function to recognize an anonymous function
> declared as a hash value?

AFAIK, you cannot. It's one of those nasty corners of Perl syntax
where to do the "right thing" would require unlimited lookahead (or
roll-back) in the parser. Perl doesn't even try - it's just
documented as a limitation.

> print( sort &{$hash{my_sort_sub}} @my_array );

my $sort_sub = $hash{my_sort_sub};
print( sort $sort_sub @my_array );

> Array found where operator expected at ./test.pl line 9, near "} "
> (Missing operator before ?)
> syntax error at ./test.pl line 9, near "} @my_array "

> Help! I don't see what's wrong with this.

The syntax of the Perl sort function is explained in

perldoc -f sort

This newsgroup does not exist (see FAQ). Please do not start threads
here.

Re: How do I call sort with an anonymous subroutine stored in a hash ??
 

you are dereferencing the anonymous subroutine incorrectly.

On line 9 you have:
print( sort &{$hash{my_sort_sub}} @my_array );

It should be:
print( sort {&{$hash{my_sort_sub}}} @my_array );

hope this helps,
Anthony



Casey <mail@nowhere.com> wrote in message news:<pan.2004.01.30.07.28.21.56357@nowhere.com>.. .
> Hi, I haven't being using perl for too long. Can someone explain the
> correct way to get the sort function to recognize an anonymous function
> declared as a hash value? Look at my sample code for clarification:
>
> #!/usr/bin/perl
>
> @my_array = qw( g a z f u q m i e b );
> $hash{my_sort_sub} = sub { $a cmp $b };
> $hash{test_routine} = sub { print "test_routine works\n" };
> &{$hash{test_routine}};
> print @my_array;
> print "\n";
> print( sort &{$hash{my_sort_sub}} @my_array );
> print "\n";
>
>
> The code fails to compile with error:
>
> Array found where operator expected at ./test.pl line 9, near "} "
> (Missing operator before ?)
> syntax error at ./test.pl line 9, near "} @my_array "
> Execution of ./test.pl aborted due to compilation errors.
>
> Help! I don't see what's wrong with this.

Re: How do I call sort with an anonymous subroutine stored in a hash ??
 

On Fri, 30 Jan 2004 04:03:25 -0800, nobull wrote:

> Casey <mail@nowhere.com> wrote in message news:<pan.2004.01.30.07.28.21.56357@nowhere.com>.. .
>> Can someone explain the
>> correct way to get the sort function to recognize an anonymous function
>> declared as a hash value?
>
> AFAIK, you cannot. It's one of those nasty corners of Perl syntax
> where to do the "right thing" would require unlimited lookahead (or
> roll-back) in the parser. Perl doesn't even try - it's just
> documented as a limitation.
>
>> print( sort &{$hash{my_sort_sub}} @my_array );
>
> my $sort_sub = $hash{my_sort_sub};
> print( sort $sort_sub @my_array );
>
>> Array found where operator expected at ./test.pl line 9, near "} "
>> (Missing operator before ?)
>> syntax error at ./test.pl line 9, near "} @my_array "
>
>> Help! I don't see what's wrong with this.
>
> The syntax of the Perl sort function is explained in
>
> perldoc -f sort
>
> This newsgroup does not exist (see FAQ). Please do not start threads
> here.

Thanks for the solution. Have a good day.