http://qs1969.pair.com?node_id=854995


in reply to make subroutine that takes expression as implicit block as first arg

You can accomplish your task using Prototypes. In fact, from the linked documentation,
here's a reimplementation of the Perl grep operator: 

sub mygrep (&@) {
    my $code = shift;
    my @result;
    foreach $_ (@_) {
        push(@result, $_) if &$code;
    }
    @result;
}

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Update: Your example would be called as: print join ",", mygrep {$_ % 2 == 0} 0..10; Note the deviation from the proposed use case. I'd initially missed the spec for "automatically put [ting] it in an implicit block"

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Re^2: make subroutine that takes expression as implicit block as first arg
by oko1 (Deacon) on Aug 13, 2010 at 19:54 UTC

    That won't work, for the proposed case: 

    Type of arg 1 to main::mygrep must be block or sub {} (not numeric eq 
+(==)) at /tmp/mygrep line 7, near "10)"
Execution of /tmp/mygrep aborted due to compilation errors.

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    Perhaps something like this? 

    sub mygrep { my $s = "grep $_[0]"; eval $s; }

print for mygrep('$_ % 2 == 0, 0..10');    # :-)

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    --
    "Language shapes the way we think, and determines what we can think about."
    -- B. L. Whorf
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[d/l]
[select]
      I added a use case, as this sort of structure is a bit sensitive - perl apparently interprets the OP proposed use case as an anonymous hash because parentheses are present.

      When I was going through a clever phase, I played a bit with prototypes, and decided they are generally more trouble than they are worth. IMHO, of course.

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