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Re: Perl 6 is too complex

by enoch (Chaplain)
on Mar 14, 2003 at 17:45 UTC ( #243130=note: print w/replies, xml ) Need Help??

in reply to Perl 6 is too complex

I had the same initial reaction as AnonyMonk when I read it. But, then I found this little Perl 6 gem of code (formatting slightly changed):

my @squares := apply { $_ * $_ } 2..5; multi apply(&func, *$head, *@tail) { return func($head), apply(&func <== @tail); }

That looked really nice to me. It was inherently perl-ish and elegant. As a mental exercise, I converted that Perl 6 code to Perl 5 best I could and came up with:

my @squares = apply(sub{$_[0] * $_[0]}, \(2..5)); sub apply { my($sub, $refArray) = @_; return map {$sub->($_)} @$refArray; }

As you can see, both pieces of code, version 5 and version 6, are remarkably similar. The Perl 6 version looks a little more tweaked... a little nicer... a little more elegant. Well... it looks like the appropriate evolution from Perl 5 to me.

After reading the Apocalypse, I wrote up a summary of all of (what I thought were) Larry's major points here. I just wanted to keep track of them, and others might find the summary useful.


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Re: Re: Perl 6 is too complex
by broquaint (Abbot) on Mar 14, 2003 at 18:44 UTC
    I converted that Perl 6 code to Perl 5 best I could and came up with
    Here's a slightly more direct conversion
    sub apply(&@) { ## ack, Class::Multimethods doesn't do variadic args :-/ return if @_ == 1; my($func, $head, @tail) = @_; local $_ = $head; return $func->(), apply($func, @tail); } my @squares = apply { $_ * $_ } 2 .. 5; print join(', ', @squares), $/; __output__ 4, 9, 16, 25
    As the comment gives away, this isn't a direct conversion as it isn't using multimethods, so it uses an arg count hack to emulate the behaviour. Also to be an even closer conversion would require apply to tie @squares to a square generator (at least I think that's probably the closest thing you can get to binding to a lazy list in perl6 with raw perl5). So it's certainly no easy task to convert that wee but powerful snippet directly to perl5!


      Also to be an even closer conversion would require apply to tie @squares to a square generator
      Ok, perhaps not a square generator, but maybe something like this
      use strict; { package Tie::Array::Apply; use overload '@{}' => sub { $_[0]->{list} }, fallback => 1; use Tie::Array; @Tie::Array::Apply::ISA = qw( Tie::StdArray ); sub TIEARRAY { my $class = shift; bless { func => shift, list => [@_], array => []}, $class; } sub FETCH { my($self,$pos) = @_; return $self->{array}->[$pos] if exists $self->{array}->[$pos]; return undef if $pos >= @{ $self->{list} }; local $_ = $self->{list}->[$pos]; return $self->{array}->[$pos] = $self->{func}->(); } } sub bind_apply(&@) { tie my @ret, 'Tie::Array::Apply', @_; return @ret; } my @bind_squares = bind_apply { $_ * $_ } 2 .. 5; print "bind_apply: ", join(', ', @bind_squares), $/; __output__ bind_apply: 4, 9, 16, 25
      That code will lazily evaluate a list where each indice is bound to a function which has the appropriate element in the initial list applied to it. But now it doesn't have the recursive behaviour demonstrated in the original perl6 function so no longer needs a funky prototype or multimethod dispatch. Ho hum.


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