10 use B qw/class ppname svref_2object OPf_KIDS/;
14 Sub::Nary - Try to count how many elements a subroutine can return in list context.
31 my $sn = Sub::Nary->new;
32 my $r = $sn->nary(\&hlagh);
36 This module uses the L<B> framework to walk into subroutines and try to guess how many scalars are likely to be returned in list context.
37 It's not always possible to give a definitive answer to this question at compile time, so the results are given in terms of "probability of return" (to be understood in a sense described below).
43 my $sn = Sub::Nary->new;
45 The usual constructor.
46 Currently takes no argument.
50 my $res = $sn->nary($coderef);
52 Takes a reference to a named or anonymous subroutine, and returns a hash reference whose keys are the possible numbers of returning scalars, and the corresponding values the "probability" to get them.
53 The special key C<'list'> is used to denote a possibly infinite number of returned arguments.
54 The return value hence would look at
56 { 1 => 0.2, 2 => 0.4, 4 => 0.3, list => 0.1 }
58 that is, we should get C<1> scalar C<1> time over C<5> and so on.
59 The sum of all values is C<1>.
60 The returned result, and all the results obtained from intermediate subs, are cached into the object.
64 Flushes the L<Sub::Nary> object cache.
65 Returns the object itself.
67 =head1 PROBABILITY OF RETURN
69 The probability is computed as such :
75 When branching, each branch is considered equally possible.
77 For example, the subroutine
87 is seen returning one or two arguments each with probability C<1/2>.
99 it is considered to return C<3> scalars with probability C<1/2>, C<2> with probability C<1/2 * 1/2 = 1/4> and C<1> (when the two tests fail, the last computed value is returned, which here is C<< $x > 0.9 >> evaluated in the scalar context of the test) with remaining probability C<1/4>.
103 The total probability law for a given returning point is the convolution product of the probabilities of its list elements.
108 return 1, simple(), 2
111 returns C<3> or C<4> arguments with probability C<1/2> ; and
114 return simple(), simple()
117 never returns C<1> argument but returns C<2> with probability C<1/2 * 1/2 = 1/4>, C<3> with probability C<1/2 * 1/2 + 1/2 * 1/2 = 1/2> and C<4> with probability C<1/4> too.
121 If a core function may return different numbers of scalars, each kind is considered equally possible.
123 For example, C<stat> returns C<13> elements on success and C<0> on error.
124 The according probability will then be C<< { 0 => 0.5, 13 => 0.5 } >>.
128 The C<list> state is absorbing in regard of all the other ones.
130 This is just a pedantic way to say that "list + fixed length = list".
134 return 1, simple(), @_
137 is considered as always returning an unbounded list.
139 Also, the convolution law does not behave the same when C<list> elements are involved : in the following example,
150 return oneorlist(), oneorlist()
153 C<composed> returns C<2> scalars with probability C<1/2 * 1/2 = 1/4> and a C<list> with probability C<3/4>.
161 XSLoader::load(__PACKAGE__, $VERSION);
165 croak 'First argument isn\'t a valid ' . __PACKAGE__ . ' object'
166 unless ref $_[0] and $_[0]->isa(__PACKAGE__);
171 $class = ref($class) || $class || __PACKAGE__;
172 bless { cache => { } }, $class;
178 $self->{cache} = { };
187 return ($self->enter(svref_2object($sub)))[1];
191 local $SIG{__DIE__} = \&Carp::confess;
193 $n eq 'null' ? substr(ppname($_[0]->targ), 3) : $n
197 my ($p, $n, $c) = @_;
198 return unless defined $p;
199 return { 0 => $c } unless $n;
201 my $z = delete $p->{0};
202 return { 'list' => $c } unless $z;
203 return { 0 => $c } if $z == 1;
204 return { 0 => $c * $z, list => $c * (1 - $z) };
206 my $r = combine map { { %$p } } 1 .. $n;
207 $r->{$_} *= $c for keys %$r;
213 $ops{$_} = 1 for scalops;
214 $ops{$_} = 0 for qw/stub nextstate pushmark iter unstack/;
215 $ops{$_} = 1 for qw/padsv/;
216 $ops{$_} = 'list' for qw/padav/;
217 $ops{$_} = 'list' for qw/padhv rv2hv/;
218 $ops{$_} = 'list' for qw/padany/;
219 $ops{$_} = 'list' for qw/match entereval readline/;
221 $ops{each} = { 0 => 0.5, 2 => 0.5 };
222 $ops{stat} = { 0 => 0.5, 13 => 0.5 };
224 $ops{caller} = sub { my @a = caller 0; scalar @a }->();
225 $ops{localtime} = do { my @a = localtime; scalar @a };
226 $ops{gmtime} = do { my @a = gmtime; scalar @a };
228 $ops{$_} = { 0 => 0.5, 10 => 0.5 } for map "gpw$_", qw/nam uid ent/;
229 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for map "ggr$_", qw/nam gid ent/;
230 $ops{$_} = 'list' for qw/ghbyname ghbyaddr ghostent/;
231 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gnbyname gnbyaddr gnetent/;
232 $ops{$_} = { 0 => 0.5, 3 => 0.5 } for qw/gpbyname gpbynumber gprotoent/;
233 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gsbyname gsbyport gservent/;
236 my ($self, $cv) = @_;
238 return undef, 'list' if class($cv) ne 'CV';
242 return undef, { %{$self->{cache}->{$tag}} } if exists $self->{cache}->{$tag};
244 # Anything can happen with recursion
245 for (@{$self->{cv}}) {
246 return undef, 'list' if $tag == tag($_->ROOT);
249 unshift @{$self->{cv}}, $cv;
250 my $r = add $self->inspect($op->first);
251 shift @{$self->{cv}};
253 $self->{cache}->{$tag} = { %$r };
258 my ($self, $op) = @_;
261 return add($self->inspect_kids($op)), undef if $n eq 'return';
263 my $meth = $self->can('pp_' . $n);
264 return $self->$meth($op) if $meth;
266 if (exists $ops{$n}) {
268 $l = { %$l } if ref $l;
272 if (class($op) eq 'LOGOP' and not null $op->first) {
276 my ($r1, $l1) = $self->inspect($op);
277 return $r1, $l1 if defined $r1 and zero $l1;
281 my ($r2, $l2) = $self->inspect($op);
286 # If the logop has no else branch, it can also return the *scalar* result of
290 ($r3, $l3) = $self->inspect($op);
293 my $r = add $r1, scale $c / 2, add $r2, $r3;
294 my $l = scale $c / 2, add $l2, $l3;
298 return $self->inspect_kids($op);
302 my ($self, $op) = @_;
304 return undef, 0 unless $op->flags & OPf_KIDS;
307 return undef, 0 if null $op;
308 if (name($op) eq 'pushmark') {
310 return undef, 0 if null $op;
315 for (; not null $op; $op = $op->sibling) {
317 if ($n eq 'nextstate') {
321 if ($n eq 'lineseq') {
326 my ($rc, $lc) = $self->inspect($op);
328 $r = add $r, scale $c, $rc if defined $rc;
329 if (not defined $lc) {
333 push @l, scale $c, $lc;
336 my $l = scale +(1 - count $r), normalize combine @l;
341 # Stolen from B::Deparse
343 sub padval { $_[0]->{cv}->[0]->PADLIST->ARRAYelt(1)->ARRAYelt($_[1]) }
346 my ($self, $op) = @_;
347 if (class($op) eq 'PADOP') {
348 return $self->padval($op->padix)
349 } else { # class($op) eq "SVOP"
355 my ($self, $op) = @_;
357 # the constant could be in the pad (under useithreads)
358 $sv = $self->padval($op->targ) unless $$sv;
363 my ($self, $op) = @_;
365 $op = $op->first while $op->flags & OPf_KIDS;
366 # First must be a pushmark
368 # Next must be non null - at worse it's the rv2cv
372 for (; not null $op->sibling; $op = $op->sibling) {
373 my ($rc, $lc) = $self->inspect($op);
374 return $rc, $lc if defined $rc and not defined $lc;
375 $r = add $r, scale $c, $rc;
379 if (name($op) eq 'rv2cv') {
383 my $next = $op->sibling;
384 while (not null $next) {
386 $next = $next->sibling;
389 } while ($op->flags & OPf_KIDS and { map { $_ => 1 } qw/null leave/ }->{$n});
390 return 'list', undef unless { map { $_ => 1 } qw/gv refgen/ }->{$n};
391 local $self->{sub} = 1;
392 my ($rc, $lc) = $self->inspect($op);
393 return $r, scale $c, $lc;
396 return $r, { 'list' => $c };
401 my ($self, $op) = @_;
403 return $self->{sub} ? $self->enter($self->gv_or_padgv($op)->CV) : (undef, 1)
407 my ($self, $op) = @_;
409 return $self->{sub} ? $self->enter($self->const_sv($op)) : (undef, 1)
413 my ($self, $op) = @_;
416 while ($op->flags & OPf_KIDS) {
417 my $nop = $op->first;
419 if ($nn eq 'pushmark') {
420 $nop = $nop->sibling;
423 if ($n eq 'rv2cv' and $nn eq 'gv') {
424 return $self->enter($self->gv_or_padgv($nop)->CV);
430 return undef, 'list';
434 my ($self, $op) = @_;
436 return undef, 0 unless $op->isa('B::SVOP');
438 my $sv = $self->const_sv($op);
443 } elsif ($c eq 'HV') {
450 sub pp_aslice { $_[0]->inspect($_[1]->first->sibling) }
453 *pp_hslice = *pp_aslice{CODE};
455 sub pp_lslice { $_[0]->inspect($_[1]->first) }
458 my ($self, $op) = @_;
461 if (name($op) eq 'gv') {
462 return undef, { list => 1 };
469 my ($self, $op) = @_;
471 my $r = ($self->inspect($op->first))[0];
473 my $c = 1 - count $r;
474 return $r, $c ? { 1 => $c } : undef
478 my ($self, $op) = @_;
482 # Can't assign to return
483 my $l = ($self->inspect($op->sibling))[1];
484 return undef, $l if not exists $l->{list};
490 my ($self, $op) = @_;
495 if (name($op) eq 'enteriter') { # for loop ?
497 ($r1, $l1) = $self->inspect($op);
498 return $r1, $l1 if defined $r1 and zero $l1;
503 if (name($op->first) eq 'and') {
504 ($r2, $l2) = $self->inspect($op->first->first);
505 return $r2, $l2 if defined $r2 and zero $l2;
507 return { list => 1 }, undef if !$for and defined $r2;
508 my ($r3, $l3) = $self->inspect($op->first->first->sibling);
509 return { list => 1 }, undef if defined $r3 and defined $l3;
510 $r2 = add $r2, scale $c, $r3;
512 ($r2, $l2) = $self->inspect($op);
513 return { list => 1 }, undef if defined $r2 and defined $l2;
516 my $r = (defined $r1) ? add $r1, scale +(1 - count $r1), $r2
518 my $c = 1 - count $r;
519 return $r, $c ? { 0 => $c } : undef;
523 my ($self, $op) = @_;
526 return $self->inspect($op) if name($op) ne 'range';
529 my $begin = $op->first;
530 if (name($begin) eq 'const') {
531 my $end = $begin->sibling;
532 if (name($end) eq 'const') {
533 $begin = $self->const_sv($begin);
534 $end = $self->const_sv($end);
536 no warnings 'numeric';
537 $begin = int ${$begin->object_2svref};
538 $end = int ${$end->object_2svref};
540 return undef, $end - $begin + 1;
542 ($r, $l) = $self->inspect($end);
545 ($r, $l) = $self->inspect($begin);
548 my $c = 1 - count $r;
549 return $r, $c ? { 'list' => $c } : undef
553 my ($self, $op) = @_;
556 return $self->inspect($op) if name($op) ne 'grepstart';
557 $op = $op->first->sibling;
559 my ($r2, $l2) = $self->inspect($op->sibling);
560 return $r2, $l2 if defined $r2 and zero $l2;
561 my $c2 = count $l2; # First one to happen
563 my ($r1, $l1) = $self->inspect($op);
564 return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
568 $l2 = { $l2 => 1 } unless ref $l2;
571 add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
572 my $c = 1 - count $r;
573 return $r, $c ? { ((zero $l2) ? 0 : 'list') => $c } : undef;
577 my ($self, $op) = @_;
580 return $self->inspect($op) if name($op) ne 'mapstart';
581 $op = $op->first->sibling;
583 my ($r2, $l2) = $self->inspect($op->sibling);
584 return $r2, $l2 if defined $r2 and zero $l2;
585 my $c2 = count $l2; # First one to happen
587 my ($r1, $l1) = $self->inspect($op);
588 return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
592 $l2 = { $l2 => 1 } unless ref $l2;
595 add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
596 my $c = 1 - count $r;
597 my $l = scale $c, normalize add map { power $l1, $_, $l2->{$_} } keys %$l2;
603 An object-oriented module shouldn't export any function, and so does this one.
607 The algorithm may be pessimistic (things seen as C<list> while they are of fixed length) but not optimistic (the opposite, duh).
609 C<wantarray> isn't specialized when encountered in the optree.
615 L<Carp> (standard since perl 5), L<B> (since perl 5.005) and L<XSLoader> (since perl 5.006).
619 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
621 You can contact me by mail or on C<irc.perl.org> (vincent).
625 Please report any bugs or feature requests to C<bug-sub-nary at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Sub-Nary>.
626 I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
630 You can find documentation for this module with the perldoc command.
634 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Sub-Nary>.
636 =head1 ACKNOWLEDGEMENTS
638 Thanks to Sebastien Aperghis-Tramoni for helping to name this module.
640 =head1 COPYRIGHT & LICENSE
642 Copyright 2008 Vincent Pit, all rights reserved.
644 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
648 1; # End of Sub::Nary