Closures in Perl

• There is actually nothing seriously wrong with them

     # Perl version                  # SML version

     sub outer {                     fun outer x' =
       my $x = shift;                  let val x = ref x'
       my $inner = sub {                   fun inner y =
         my $y = shift;  
         if ($y == 0) { $x++ }                ((if y = 0 then x:= !x+1 else ());
         return $x + $y;                       b + !x)
       };                              in
       return $inner;                       inner
     }                                 end

     my $d = outer(100);               val d = outer 100
     my $e = outer(10);                val e = outer 10

     $d->(3);                       # returns 103
     $e->(3);                       # returns 13
     $d->(0);                       # returns 101
     $d->(3);                       # returns 104
     $e->(3);                       # returns 13

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Copyright 2005 M. J. Dominus