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. 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).
42 The usual constructor. Currently takes no argument.
44 =head2 C<nary $coderef>
46 Takes a code 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. A few special keys are also used :
52 C<'list'> is used to denote a possibly infinite number of returned arguments ;
56 C<'exit'> gives the probability for C<exit> to be called somewhere in the code.
60 The return value hence would look at
62 { 1 => 0.2, 2 => 0.4, 4 => 0.25, list => 0.1, exit => 0.05 }
64 that is, we should get C<1> scalar C<1> time over C<5> and so on. The sum of all values is C<1>. The returned result, and all the results obtained from intermediate subs, are cached into the object.
68 Flushes the L<Sub::Nary> object cache. Returns the object itself.
70 =head1 PROBABILITY OF RETURN
72 The probability is computed as such :
76 =item * When branching, each branch is considered equally possible.
78 For example, the subroutine
88 is seen returning one or two arguments each with probability C<1/2>.
100 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>.
102 =item * The total probability law for a given returning point is the convolution product of the probabilities of its list elements.
107 return 1, simple(), 2
110 returns C<3> or C<4> arguments with probability C<1/2> ; and
113 return simple(), simple()
116 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.
118 =item * If a core function may return different numbers of scalars, each kind is considered equally possible.
120 For example, C<stat> returns C<13> elements on success and C<0> on error. The according probability will then be C<< { 0 => 0.5, 13 => 0.5 } >>.
122 =item * The C<list> and C<exit> states are absorbing in regard of all the other ones.
124 This is just a pedantic way to say that C<list + fixed length = list>, C<exit + fixed length = exit>, but note also that C<exit + list = exit>.
128 return 1, simple(), @_
131 is considered as always returning an unbounded list.
133 Also, the convolution law does not behave the same when C<list> or C<exit> elements are involved : in the following example,
144 return oneorlist(), oneorlist()
147 C<composed> returns C<2> scalars with probability C<1/2 * 1/2 = 1/4> and a C<list> with probability C<3/4>.
155 XSLoader::load(__PACKAGE__, $VERSION);
159 croak 'First argument isn\'t a valid ' . __PACKAGE__ . ' object'
160 unless ref $_[0] and $_[0]->isa(__PACKAGE__);
165 $class = ref($class) || $class || __PACKAGE__;
166 bless { cache => { } }, $class;
172 $self->{cache} = { };
181 return ($self->enter(svref_2object($sub)))[1];
185 local $SIG{__DIE__} = \&Carp::confess;
187 $n eq 'null' ? substr(ppname($_[0]->targ), 3) : $n
191 my ($p, $n, $c) = @_;
192 return unless defined $p;
193 return { 0 => $c } unless $n;
195 my $z = delete $p->{0};
196 return { 'list' => $c } unless $z;
197 return { 0 => $c } if $z == 1;
198 return { 0 => $c * $z, list => $c * (1 - $z) };
200 my $r = combine map { { %$p } } 1 .. $n;
201 $r->{$_} *= $c for keys %$r;
207 $ops{$_} = 1 for scalops;
208 $ops{$_} = 0 for qw/stub nextstate pushmark iter unstack/;
209 $ops{$_} = 1 for qw/padsv/;
210 $ops{$_} = 'list' for qw/padav/;
211 $ops{$_} = 'list' for qw/padhv rv2hv/;
212 $ops{$_} = 'list' for qw/padany/;
213 $ops{$_} = 'list' for qw/match entereval readline/;
215 $ops{each} = { 0 => 0.5, 2 => 0.5 };
216 $ops{stat} = { 0 => 0.5, 13 => 0.5 };
218 $ops{caller} = sub { my @a = caller 0; scalar @a }->();
219 $ops{localtime} = do { my @a = localtime; scalar @a };
220 $ops{gmtime} = do { my @a = gmtime; scalar @a };
222 $ops{$_} = { 0 => 0.5, 10 => 0.5 } for map "gpw$_", qw/nam uid ent/;
223 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for map "ggr$_", qw/nam gid ent/;
224 $ops{$_} = 'list' for qw/ghbyname ghbyaddr ghostent/;
225 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gnbyname gnbyaddr gnetent/;
226 $ops{$_} = { 0 => 0.5, 3 => 0.5 } for qw/gpbyname gpbynumber gprotoent/;
227 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gsbyname gsbyport gservent/;
230 my ($self, $cv) = @_;
232 return undef, 'list' if class($cv) ne 'CV';
236 return undef, { %{$self->{cache}->{$tag}} } if exists $self->{cache}->{$tag};
238 # Anything can happen with recursion
239 for (@{$self->{cv}}) {
240 return undef, 'list' if $tag == tag($_->ROOT);
243 unshift @{$self->{cv}}, $cv;
244 my $r = add $self->inspect($op->first);
245 shift @{$self->{cv}};
247 $self->{cache}->{$tag} = { %$r };
252 my ($self, $op) = @_;
255 return add($self->inspect_kids($op)), undef if $n eq 'return';
257 my $meth = $self->can('pp_' . $n);
258 return $self->$meth($op) if $meth;
260 if (exists $ops{$n}) {
262 $l = { %$l } if ref $l;
266 if (class($op) eq 'LOGOP' and not null $op->first) {
270 my ($r1, $l1) = $self->inspect($op);
271 return $r1, $l1 if defined $r1 and zero $l1;
275 my ($r2, $l2) = $self->inspect($op);
280 # If the logop has no else branch, it can also return the *scalar* result of
284 ($r3, $l3) = $self->inspect($op);
287 my $r = add $r1, scale $c / 2, add $r2, $r3;
288 my $l = scale $c / 2, add $l2, $l3;
292 return $self->inspect_kids($op);
296 my ($self, $op) = @_;
298 return undef, 0 unless $op->flags & OPf_KIDS;
301 return undef, 0 if null $op;
302 if (name($op) eq 'pushmark') {
304 return undef, 0 if null $op;
309 for (; not null $op; $op = $op->sibling) {
311 if ($n eq 'nextstate') {
315 if ($n eq 'lineseq') {
320 my ($rc, $lc) = $self->inspect($op);
322 $r = add $r, scale $c, $rc if defined $rc;
323 if (not defined $lc) {
327 push @l, scale $c, $lc;
330 my $l = scale +(1 - count $r), normalize combine @l;
335 # Stolen from B::Deparse
337 sub padval { $_[0]->{cv}->[0]->PADLIST->ARRAYelt(1)->ARRAYelt($_[1]) }
340 my ($self, $op) = @_;
341 if (class($op) eq 'PADOP') {
342 return $self->padval($op->padix)
343 } else { # class($op) eq "SVOP"
349 my ($self, $op) = @_;
351 # the constant could be in the pad (under useithreads)
352 $sv = $self->padval($op->targ) unless $$sv;
357 my ($self, $op) = @_;
359 $op = $op->first while $op->flags & OPf_KIDS;
360 # First must be a pushmark
362 # Next must be non null - at worse it's the rv2cv
366 for (; not null $op->sibling; $op = $op->sibling) {
367 my ($rc, $lc) = $self->inspect($op);
368 return $rc, $lc if defined $rc and not defined $lc;
369 $r = add $r, scale $c, $rc;
373 if (name($op) eq 'rv2cv') {
377 my $next = $op->sibling;
378 while (not null $next) {
380 $next = $next->sibling;
383 } while ($op->flags & OPf_KIDS and { map { $_ => 1 } qw/null leave/ }->{$n});
384 return 'list', undef unless { map { $_ => 1 } qw/gv refgen/ }->{$n};
385 local $self->{sub} = 1;
386 my ($rc, $lc) = $self->inspect($op);
387 return $r, scale $c, $lc;
390 return $r, { 'list' => $c };
395 my ($self, $op) = @_;
397 return $self->{sub} ? $self->enter($self->gv_or_padgv($op)->CV) : (undef, 1)
401 my ($self, $op) = @_;
403 return $self->{sub} ? $self->enter($self->const_sv($op)) : (undef, 1)
407 my ($self, $op) = @_;
410 if ($op->flags & OPf_KIDS) {
411 ($r, my $l) = $self->inspect($op->first);
412 return $r, $l if defined $r and zero $l;
413 $r->{exit} = 1 - count $r;
415 $r = { 'exit' => 1 };
422 my ($self, $op) = @_;
425 while ($op->flags & OPf_KIDS) {
426 my $nop = $op->first;
428 if ($nn eq 'pushmark') {
429 $nop = $nop->sibling;
432 if ($n eq 'rv2cv' and $nn eq 'gv') {
433 return $self->enter($self->gv_or_padgv($nop)->CV);
439 return undef, 'list';
443 my ($self, $op) = @_;
445 return undef, 0 unless $op->isa('B::SVOP');
447 my $sv = $self->const_sv($op);
452 } elsif ($c eq 'HV') {
459 sub pp_aslice { $_[0]->inspect($_[1]->first->sibling) }
462 *pp_hslice = *pp_aslice{CODE};
464 sub pp_lslice { $_[0]->inspect($_[1]->first) }
467 my ($self, $op) = @_;
470 if (name($op) eq 'gv') {
471 return undef, { list => 1 };
478 my ($self, $op) = @_;
480 my $r = ($self->inspect($op->first))[0];
482 my $c = 1 - count $r;
483 return $r, $c ? { 1 => $c } : undef
487 my ($self, $op) = @_;
491 # Can't assign to return
492 my $l = ($self->inspect($op->sibling))[1];
493 return undef, $l if not exists $l->{list};
499 my ($self, $op) = @_;
504 if (name($op) eq 'enteriter') { # for loop ?
506 ($r1, $l1) = $self->inspect($op);
507 return $r1, $l1 if defined $r1 and zero $l1;
512 if (name($op->first) eq 'and') {
513 ($r2, $l2) = $self->inspect($op->first->first);
514 return $r2, $l2 if defined $r2 and zero $l2;
516 return { list => 1 }, undef if !$for and defined $r2;
517 my ($r3, $l3) = $self->inspect($op->first->first->sibling);
518 return { list => 1 }, undef if defined $r3 and defined $l3;
519 $r2 = add $r2, scale $c, $r3;
521 ($r2, $l2) = $self->inspect($op);
522 return { list => 1 }, undef if defined $r2 and defined $l2;
525 my $r = (defined $r1) ? add $r1, scale +(1 - count $r1), $r2
527 my $c = 1 - count $r;
528 return $r, $c ? { 0 => $c } : undef;
532 my ($self, $op) = @_;
535 return $self->inspect($op) if name($op) ne 'range';
538 my $begin = $op->first;
539 if (name($begin) eq 'const') {
540 my $end = $begin->sibling;
541 if (name($end) eq 'const') {
542 $begin = $self->const_sv($begin);
543 $end = $self->const_sv($end);
545 no warnings 'numeric';
546 $begin = int ${$begin->object_2svref};
547 $end = int ${$end->object_2svref};
549 return undef, $end - $begin + 1;
551 ($r, $l) = $self->inspect($end);
554 ($r, $l) = $self->inspect($begin);
557 my $c = 1 - count $r;
558 return $r, $c ? { 'list' => $c } : undef
562 my ($self, $op) = @_;
565 return $self->inspect($op) if name($op) ne 'grepstart';
566 $op = $op->first->sibling;
568 my ($r2, $l2) = $self->inspect($op->sibling);
569 return $r2, $l2 if defined $r2 and zero $l2;
570 my $c2 = count $l2; # First one to happen
572 my ($r1, $l1) = $self->inspect($op);
573 return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
577 $l2 = { $l2 => 1 } unless ref $l2;
580 add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
581 my $c = 1 - count $r;
582 return $r, $c ? { ((zero $l2) ? 0 : 'list') => $c } : undef;
586 my ($self, $op) = @_;
589 return $self->inspect($op) if name($op) ne 'mapstart';
590 $op = $op->first->sibling;
592 my ($r2, $l2) = $self->inspect($op->sibling);
593 return $r2, $l2 if defined $r2 and zero $l2;
594 my $c2 = count $l2; # First one to happen
596 my ($r1, $l1) = $self->inspect($op);
597 return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
601 $l2 = { $l2 => 1 } unless ref $l2;
604 add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
605 my $c = 1 - count $r;
606 my $l = scale $c, normalize add map { power $l1, $_, $l2->{$_} } keys %$l2;
612 An object-oriented module shouldn't export any function, and so does this one.
616 The algorithm may be pessimistic (things seen as C<list> while they are of fixed length) but not optimistic (the opposite, duh).
618 C<wantarray> isn't specialized when encountered in the optree.
624 L<Carp> (standard since perl 5), L<B> (since perl 5.005) and L<XSLoader> (since perl 5.006).
628 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
630 You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).
634 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>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
638 You can find documentation for this module with the perldoc command.
642 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Sub-Nary>.
644 =head1 ACKNOWLEDGEMENTS
646 Thanks to Sebastien Aperghis-Tramoni for helping to name this module.
648 =head1 COPYRIGHT & LICENSE
650 Copyright 2008 Vincent Pit, all rights reserved.
652 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
656 1; # End of Sub::Nary