http://www.perlmonks.org?node_id=908596


in reply to (almost) foldl

Well, in unary, summing is as simple as concatenating. And Perl has a built-in decimal-to-unary converter (the x operator), as well as a built-in unary-to-decimal converter (the length function). Putting all this together: 
my @list = (1, 2, 3, 4, 5);
print length join "", map{"1" x $_} @list; #prints 15

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But your implementation sure is fun :-) EDIT: Look at tye's code instead. This one is stupid. Don't know what I had in mind when I wrote 'length join "", '.

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Re^2: (almost) foldl (""=>())
by tye (Sage) on Jun 08, 2011 at 02:24 UTC 
    my @list = ( 1..6 );
print 0+map{(1)x$_}@list;

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    - tye        

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Re^2: (almost) foldl
by dk (Chaplain) on Jun 08, 2011 at 04:56 UTC
    negative numbers?
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      my @list = ( -4 .. 6 );
print map((1)x$_,@list) - map((1)x-$_,@list);

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      - tye        

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[d/l]
        Wow. That's a exactly (and I mean, exactly) the first idea I had to solve the negative numbers problem. I didn't post it, though, because it doesn't handle decimal numbers.
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      sub sum { eval 'pop(@_)+' x ($#_ + 1) . '0'; }

@list = (-4, 15, -5, 2.5);
print sum @list;            # 8.5, as expected
print sum -4, 15, -5, 2.5;  # Works the same
print sum;                  # 0 (not undef)

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      EDIT: replaced $#list with $#_ , so that it works with lists of any length. Silly me.
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In Section Obfuscated Code