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  1. local $Y = sub {
  2.     local ($h) = @_;
  3.     sub { local ($x) = @_; $x->($x) }->(
  4.         sub {
  5.             local ($g) = @_;
  6.             $h->(sub { local @args = @_; $g->($g)->(@args) })
  7.         }
  8.     )
  9. };
  10.  
  11. local $trampoline = sub {
  12.     local ($f) = @_;
  13.     sub {
  14.         local @args = @_;
  15.         local $result = $f->(@args);
  16.         while (ref($result) eq 'CODE') {
  17.             $result = $result->();
  18.         }
  19.         $result
  20.     }
  21. };
  22.  
  23. local $fac = sub {
  24.     local ($n) = @_;
  25.     $trampoline->(
  26.         $Y->(sub {
  27.             local ($f) = @_;
  28.             sub {
  29.                 local ($n, $acc) = @_;
  30.                 $n == 0
  31.                     ? $acc
  32.                     : sub { $f->($n - 1, $n * $acc) }
  33.             }
  34.         })
  35.     )->($n, 1)
  36. };
  37.  
  38. print $fac->(5), "\n";
Runtime error #stdin #stdout #stderr 0s 17496KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
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Can't use an undefined value as a subroutine reference at prog.pl line 15.
https://ideone.com/DWjwBj
language:
Perl (perl 5.28.1)
created:
6 years ago
visibility:
public

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