9 use List::Util qw/reduce/;
11 use B qw/class ppname svref_2object OPf_KIDS/;
13 use Test::More; use Data::Dumper;
17 Sub::Nary - Try to count how many elements a subroutine can return in list context.
36 my $sn = Sub::Nary->new();
37 my $r = $sn->nary(\&hlagh);
41 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).
47 The usual constructor. Currently takes no argument.
49 =head2 C<nary $coderef>
51 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. The special key C<'list'> is used to denote a possibly infinite number of returned arguments. The return value hence would look at
53 { 1 => 0.2, 2 => 0.4, 4 => 0.3, list => 0.1 }
55 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.
59 Flushes the L<Sub::Nary> object cache. Returns the object itself.
61 =head1 PROBABILITY OF RETURN
63 The probability is computed as such :
67 =item * When branching, each branch is considered equally possible.
69 For example, the subroutine
79 is seen returning one or two arguments each with probability C<1/2>.
91 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>.
93 =item * The total probability law for a given returning point is the convolution product of the probabilities of its list elements.
101 returns C<3> or C<4> arguments with probability C<1/2> ; and
104 return simple(), simple()
107 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.
109 =item * If a core function may return different numbers of scalars, each kind is considered equally possible.
111 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 } >>.
113 =item * The C<list> state is absorbing in regard of all the other ones.
115 This is just a pedantic way to say that "list + fixed length = list".
119 return 1, simple(), @_
122 is considered as always returning an unbounded list.
124 Also, the convolution law does not behave the same when C<list> elements are involved : in the following example,
135 return oneorlist(), oneorlist()
138 C<composed> returns C<2> scalars with probability C<1/2 * 1/2 = 1/4> and a C<list> with probability C<3/4>.
146 XSLoader::load(__PACKAGE__, $VERSION);
150 croak 'First argument isn\'t a valid ' . __PACKAGE__ . ' object'
151 unless ref $_[0] and $_[0]->isa(__PACKAGE__);
156 $class = ref($class) || $class || __PACKAGE__;
157 bless { cache => { } }, $class;
163 $self->{cache} = { };
172 return ($self->enter(svref_2object($sub)))[1];
176 local $SIG{__DIE__} = \&Carp::confess;
178 $n eq 'null' ? substr(ppname($_[0]->targ), 3) : $n
182 my ($p, $n, $c) = @_;
183 return unless defined $p;
184 return { 0 => $c } unless $n;
186 my $z = delete $p->{0};
187 return { 'list' => $c } unless $z;
188 return { 0 => $c } if $z == 1;
189 return { 0 => $c * $z, list => $c * (1 - $z) };
191 my $r = combine map { { %$p } } 1 .. $n;
192 $r->{$_} *= $c for keys %$r;
198 $a->{$_} += $b->{$_} for keys %$b;
200 } map { (ref) ? $_ : { $_ => 1 } } grep defined, @_;
205 $ops{$_} = 1 for scalops;
206 $ops{$_} = 0 for qw/stub nextstate pushmark iter unstack/;
207 $ops{$_} = 1 for qw/padsv/;
208 $ops{$_} = 'list' for qw/padav/;
209 $ops{$_} = 'list' for qw/padhv rv2hv/;
210 $ops{$_} = 'list' for qw/padany/;
211 $ops{$_} = 'list' for qw/match entereval readline/;
213 $ops{each} = { 0 => 0.5, 2 => 0.5 };
214 $ops{stat} = { 0 => 0.5, 13 => 0.5 };
216 $ops{caller} = sub { my @a = caller 0; scalar @a }->();
217 $ops{localtime} = do { my @a = localtime; scalar @a };
218 $ops{gmtime} = do { my @a = gmtime; scalar @a };
220 $ops{$_} = { 0 => 0.5, 10 => 0.5 } for map "gpw$_", qw/nam uid ent/;
221 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for map "ggr$_", qw/nam gid ent/;
222 $ops{$_} = 'list' for qw/ghbyname ghbyaddr ghostent/;
223 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gnbyname gnbyaddr gnetent/;
224 $ops{$_} = { 0 => 0.5, 3 => 0.5 } for qw/gpbyname gpbynumber gprotoent/;
225 $ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gsbyname gsbyport gservent/;
228 my ($self, $cv) = @_;
230 return undef, 'list' if class($cv) ne 'CV';
234 return undef, { %{$self->{cache}->{$tag}} } if exists $self->{cache}->{$tag};
236 # Anything can happen with recursion
237 for (@{$self->{cv}}) {
238 return undef, 'list' if $tag == tag($_->ROOT);
241 unshift @{$self->{cv}}, $cv;
242 my $r = add $self->inspect($op->first);
243 shift @{$self->{cv}};
245 $r = { $r => 1 } unless ref $r;
246 $self->{cache}->{$tag} = { %$r };
251 my ($self, $op) = @_;
254 diag "@ $n" if $DEBUG;
255 return add($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) {
269 diag "? logop\n" if $DEBUG;
272 my ($r1, $l1) = $self->inspect($op);
273 return $r1, $l1 if $r1 and zero $l1;
277 my ($r2, $l2) = $self->inspect($op);
282 # If the logop has no else branch, it can also return the *scalar* result of
286 ($r3, $l3) = $self->inspect($op);
289 my $r = add $r1, scale $c / 2, add $r2, $r3;
290 my $l = scale $c / 2, add $l2, $l3;
294 return $self->inspect_kids($op);
298 my ($self, $op) = @_;
300 return undef, 0 unless $op->flags & OPf_KIDS;
303 return undef, 0 if null $op;
304 if (name($op) eq 'pushmark') {
306 return undef, 0 if null $op;
311 for (; not null $op; $op = $op->sibling) {
313 if ($n eq 'nextstate') {
317 if ($n eq 'lineseq') {
322 diag "> $n ($c)" if $DEBUG;
323 my ($rc, $lc) = $self->inspect($op);
324 $r = add $r, scale $c, $rc if defined $rc;
325 if ($rc and not defined $lc) {
329 push @l, scale $c, $lc;
330 $c *= count $lc if defined $lc;
338 # Stolen from B::Deparse
340 sub padval { $_[0]->{cv}->[0]->PADLIST->ARRAYelt(1)->ARRAYelt($_[1]) }
343 my ($self, $op) = @_;
344 if (class($op) eq 'PADOP') {
345 return $self->padval($op->padix)
346 } else { # class($op) eq "SVOP"
352 my ($self, $op) = @_;
354 # the constant could be in the pad (under useithreads)
355 $sv = $self->padval($op->targ) unless $$sv;
360 my ($self, $op) = @_;
362 $op = $op->first while $op->flags & OPf_KIDS;
363 return undef, 0 if null $op;
364 if (name($op) eq 'pushmark') {
366 return undef, 0 if null $op;
371 for (; not null $op->sibling; $op = $op->sibling) {
373 next if $n eq 'nextstate';
374 diag "* $n" if $DEBUG;
375 my ($rc, $lc) = $self->inspect($op);
376 $r = add $r, scale $c, $rc if defined $rc;
379 return $r, $c ? { 0 => $c } : undef
384 if (name($op) eq 'rv2cv') {
388 my $next = $op->sibling;
389 while (not null $next) {
391 $next = $next->sibling;
394 } while ($op->flags & OPf_KIDS and { map { $_ => 1 } qw/null leave/ }->{$n});
395 return 'list', undef unless { map { $_ => 1 } qw/gv refgen/ }->{$n};
396 local $self->{sub} = 1;
397 my ($rc, $lc) = $self->inspect($op);
398 return $r, scale $c, $lc;
401 return $r, { 'list' => $c };
406 my ($self, $op) = @_;
408 return $self->{sub} ? $self->enter($self->gv_or_padgv($op)->CV) : (undef, 1)
412 my ($self, $op) = @_;
414 return $self->{sub} ? $self->enter($self->const_sv($op)) : (undef, 1)
418 my ($self, $op) = @_;
421 while ($op->flags & OPf_KIDS) {
422 my $nop = $op->first;
424 if ($nn eq 'pushmark') {
425 $nop = $nop->sibling;
428 if ($n eq 'rv2cv' and $nn eq 'gv') {
429 return $self->enter($self->gv_or_padgv($nop)->CV);
435 return undef, 'list';
439 my ($self, $op) = @_;
441 return undef, 0 unless $op->isa('B::SVOP');
443 my $sv = $self->const_sv($op);
448 } elsif ($c eq 'HV') {
455 sub pp_aslice { $_[0]->inspect($_[1]->first->sibling) }
458 *pp_hslice = *pp_aslice{CODE};
460 sub pp_lslice { $_[0]->inspect($_[1]->first) }
463 my ($self, $op) = @_;
466 my ($r, $l) = $self->inspect($op);
467 if (name($op) ne 'const') {
468 my $c = 1 - count $r;
469 $l = $c ? { list => $c } : 0;
475 my ($self, $op) = @_;
479 # Can't assign to return
480 my $l = ($self->inspect($op->sibling))[1];
481 return undef, $l if not exists $l->{list};
487 my ($self, $op) = @_;
489 diag "* leaveloop" if $DEBUG;
493 if (name($op) eq 'enteriter') {
494 ($r1, $l1) = $self->inspect($op);
495 return $r1, $l1 if $r1 and zero $l1;
499 my $r = (name($op->first) eq 'and') ? ($self->inspect($op->first->first->sibling))[0]
500 : ($self->inspect($op))[0];
501 my $c = 1 - count $r;
502 diag "& leaveloop" if $DEBUG;
503 return $r, $c ? { 0 => $c } : undef;
507 my ($self, $op) = @_;
510 return $self->inspect($op) if name($op) ne 'range';
513 my $begin = $op->first;
514 if (name($begin) eq 'const') {
515 my $end = $begin->sibling;
516 if (name($end) eq 'const') {
517 $begin = $self->const_sv($begin);
518 $end = $self->const_sv($end);
520 no warnings 'numeric';
521 $begin = int ${$begin->object_2svref};
522 $end = int ${$end->object_2svref};
524 return undef, $end - $begin + 1;
526 ($r, $l) = $self->inspect($end);
529 ($r, $l) = $self->inspect($begin);
532 my $c = 1 - count $r;
533 return $r, ($l && $c) ? { 'list' => $c } : undef
537 my ($self, $op) = @_;
540 return $self->inspect($op) if name($op) ne 'grepstart';
541 $op = $op->first->sibling;
543 my ($r2, $l2) = $self->inspect($op->sibling);
544 return $r2, $l2 if $r2 and zero $l2;
545 diag Dumper [ $r2, $l2 ] if $DEBUG;
546 my $c = count $l2; # First one to happen
548 my ($r1, $l1) = $self->inspect($op);
549 diag Dumper [ $r1, $l1 ] if $DEBUG;
550 return (add $r2, scale $c, $r1), undef if $r1 and zero $l1 and not zero $l2;
551 return { 'list' => 1 }, undef if list $l2;
553 $l2 = { $l2 => 1 } unless ref $l2;
554 my $r = add $r2, scale $c,
556 add map { power $r1, $_, $l2->{$_} } keys %$l2;
558 return $r, $c ? { ((zero $l2) ? 0 : 'list') => $c } : undef;
562 my ($self, $op) = @_;
565 return $self->inspect($op) if name($op) ne 'mapstart';
566 $op = $op->first->sibling;
568 my ($r2, $l2) = $self->inspect($op->sibling);
569 return $r2, $l2 if $r2 and zero $l2;
570 my $c = count $l2; # First one to happen
572 my ($r1, $l1) = $self->inspect($op);
573 return (add $r2, scale $c, $r1), undef if $r1 and zero $l1 and not zero $l2;
574 diag Dumper [ [ $r1, $l1 ], [ $r2, $l2 ] ] if $DEBUG;
576 $l2 = { $l2 => 1 } unless ref $l2;
577 my $r = add $r2, scale $c,
579 add map { power $r1, $_, $l2->{$_} } keys %$l2;
581 my $l = scale $c, normalize add map { power $l1, $_, $l2->{$_} } keys %$l2;
587 An object-oriented module shouldn't export any function, and so does this one.
591 The algorithm may be pessimistic (things seen as C<list> while they are of fixed length) but not optimistic (the opposite, duh).
593 C<wantarray> isn't specialized when encountered in the optree.
599 L<Carp> (standard since perl 5), L<B> (since perl 5.005), L<XSLoader> (since perl 5.006) and L<List::Util> (since perl 5.007003).
603 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
605 You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).
609 Please report any bugs or feature requests to C<bug-b-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.
613 You can find documentation for this module with the perldoc command.
617 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Sub-Nary>.
619 =head1 ACKNOWLEDGEMENTS
621 Thanks to Sebastien Aperghis-Tramoni for helping to name this module.
623 =head1 COPYRIGHT & LICENSE
625 Copyright 2008 Vincent Pit, all rights reserved.
627 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
631 1; # End of Sub::Nary