What confuses me is that, in Prototypes, it is suggested that a function prototyped (&@) behaves like grep. However, whereas one calls 
grep &$code, @list

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to find all the elements $_ of @list for which $code->($_) is true, for a hypothetical mygrep (&@), one would call 
mygrep \&$code, @list

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to achieve the same goal.

ikegami pointed out yet another subtlety, which is that grep cannot accept a ‘calculated’ first argument. Thus, 

sub mygrep (&@) { my ( $code, @list ) = @_; return grep &$code, @list 
+}
sub gt { my ( $test ) = @_; return sub { $_ > $test } }
grep &{ gt 1 }, qw/1 2 3 1 4/; => ()
mygrep \&{ gt 1 }, qw/1 2 3 1 4/; => ( 2, 3, 4 )

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(While I'm at it, ikegami also pointed out that my first example could be written as grep $code->(), @list, which I find completely bizarre.)

UPDATE: Actually, having just run the code, it seems to me that the grep and mygrep invocations actually return the same thing (namely, (2, 3, 4)), so I must have misunderstood. Can anyone (like ikegami :-) ) clarify for me?

In reply to Re: coderefs and (&) prototypes by JadeNB
in thread coderefs and (&) prototypes by LanX

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