Sub::Suspension

[Steffen Goeldner]

Although it seems somewhat antiquated these days, I'm
interested in your opinions before uploading the module

  Sub::Suspension - Suspended subroutine.

An instance of this class behaves like a sub (-ref), but
it supports partial application and the evaluation of
operators applied to suspensions is suspended too.
That means, evaluation has to be forced explicitly (which
makes it easier to add introspection capabilities).

Regarding partial application, this module is similar to
Perl6::Currying and Sub::Curry.

  <http://search.cpan.org/~dconway/Perl6-Currying-0.05/>
  <http://search.cpan.org/~davidh/Sub-Curry-0.08/>

Application of an operator to a suspension returns another
suspension.
The Symbolic calculator example from overload.pm uses similar
mechanisms:

  <http://search.cpan.org/~nwclark/perl-5.8.4/lib/overload.pm#Symbolic_calculator>


Example:

  use Sub::Suspension 'def';

  $S = def sub : P1 P2 P3 { [EMAIL PROTECTED]; join '', @_{qw(P1 P2 P3)} };

  print $S->( P1 => 1, P2 => 2, P3 => 3 )->(); # 123

  $A = $S->( P3 => 1 );  # partial application
  $B = $S->( P3 => 2 );

  $C = $A + $B;

  $D = $C->( P2 => 3 );
  $E = $D->( P1 => 4 );

  print $E->();    # force evaluation: 863

  $F = $E - $D;

  $G = $F->( P1 => 0 ) / 2;

  print $G->();    # 400
  print $G;        # ( ( CODE(0x15e3818)( P1 => 4, P2 => 3, P3 => 1 ) + CODE ...

  $F->();          # Error: Free parameter : P1
  $A->( P3 => 7 ); # Error: Bound parameter: P3
  $A->( P4 => 7 ); # Error: Wrong parameter: P4


Related concepts are:

  thunk
  lazy evaluation
  defered evaluation
  delayed evaluation
  currying
  closure
  functor (qua function object)

but I think the name 'suspension' matches best.


Steffen