9 use List::Util qw/reduce sum/;
11 use B qw/class ppname svref_2object OPf_KIDS/;
15 Sub::Nary - Try to count how many elements a subroutine can return in list context.
32 my $sn = Sub::Nary->new();
33 my $r = $sn->nary(\&hlagh);
37 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).
43 The usual constructor. Currently takes no argument.
45 =head2 C<nary $coderef>
47 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
49 { 1 => 0.2, 2 => 0.4, 4 => 0.3, list => 0.1 }
51 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.
55 Flushes the L<Sub::Nary> object cache. Returns the object itself.
57 =head1 PROBABILITY OF RETURN
59 The probability is computed as such :
63 =item * All the returning points in the same subroutine (i.e. all the explicit C<return> and the last computed value) are considered equally possible.
65 For example, the subroutine
75 is seen returning one or two arguments each with probability C<1/2>.
87 it is considered to return 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), C<2> or C<3> arguments each with probability C<1/3>.
89 =item * The total probability law for a given returning point is the convolution product of the probabilities of its list elements.
97 returns C<3> or C<4> arguments with probability C<1/2> ; and
100 return simple(), simple()
103 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.
105 =item * The C<list> state is absorbing in regard of all the other ones.
107 This is just a pedantic way to say that "list + fixed length = list".
111 return 1, simple(), @_
114 is considered as always returning an unbounded list.
116 Also, the convolution law does not behave the same when C<list> elements are involved : in the following example,
127 return oneorlist(), oneorlist()
130 C<composed> returns C<2> scalars with probability C<1/2 * 1/2 = 1/4> and a C<list> with probability C<3/4>.
138 XSLoader::load(__PACKAGE__, $VERSION);
142 croak 'First argument isn\'t a valid ' . __PACKAGE__ . ' object'
143 unless ref $_[0] and $_[0]->isa(__PACKAGE__);
148 $class = ref($class) || $class || __PACKAGE__;
149 bless { cache => { } }, $class;
155 $self->{cache} = { };
164 return $self->enter(svref_2object($sub));
169 $n eq 'null' ? substr(ppname($_[0]->targ), 3) : $n
175 my $la = delete $a->{list};
176 my $lb = delete $b->{list};
177 if (defined $la || defined $lb) {
180 $res{list} = $la + $lb - $la * $lb;
182 while (my ($ka, $va) = each %$a) {
184 while (my ($kb, $vb) = each %$b) {
185 my $key = $ka + int $kb;
186 $res{$key} += $va * $vb;
190 }} map { (ref) ? $_ : { $_ => 1 } } grep defined, @_;
195 $a->{$_} += $b->{$_} for keys %$b;
197 } map { (ref) ? $_ : { $_ => 1 } } grep defined, @_;
201 $ops{$_} = 1 for scalops;
202 $ops{$_} = 0 for qw/stub nextstate/;
203 $ops{$_} = 1 for qw/padsv/;
204 $ops{$_} = 'list' for qw/padav/;
205 $ops{$_} = 'list' for qw/padhv rv2hv/;
206 $ops{$_} = 'list' for qw/padany flip match entereval readline/;
208 $ops{caller} = sub { my @a = caller 0; scalar @a }->();
209 $ops{localtime} = do { my @a = localtime; scalar @a };
210 $ops{gmtime} = do { my @a = gmtime; scalar @a };
213 my ($self, $cv) = @_;
215 return 'list' if class($cv) ne 'CV';
219 return { %{$self->{cache}->{$tag}} } if exists $self->{cache}->{$tag};
221 # Anything can happen with recursion
222 for (@{$self->{cv}}) {
223 return 'list' if $tag == tag($_->ROOT);
226 unshift @{$self->{cv}}, $cv;
227 (my $r, undef) = $self->expect_any($op->first);
228 shift @{$self->{cv}};
230 $r = { $r => 1} unless ref $r;
231 my $total = sum values %$r;
232 $r = { map { $_ => $r->{$_} / $total } keys %$r };
233 $self->{cache}->{$tag} = { %$r };
238 my ($self, $op) = @_;
240 return ($self->expect_list($op))[0] => 1 if name($op) eq 'return';
242 if ($op->flags & OPf_KIDS) {
243 for ($op = $op->first; not null $op; $op = $op->sibling) {
244 my ($p, $r) = $self->expect_return($op);
245 return $p => 1 if $r;
253 my ($self, $op) = @_;
256 my $meth = $self->can('pp_' . $n);
257 return $self->$meth($op) if $meth;
258 return $ops{$n} => 0 if exists $ops{$n};
260 if ($op->flags & OPf_KIDS) {
263 for ($op = $op->first; not null $op; $op = $op->sibling) {
265 next if $n eq 'pushmark';
266 if ($n eq 'nextstate'
267 and not null(($op = $op->sibling)->sibling)) {
268 ($p, $r) = $self->expect_return($op);
269 return $p => 1 if $r;
271 ($p, $r) = $self->expect_any($op);
272 return $p => 1 if $r;
276 return (combine @res) => 0;
283 my ($self, $op) = @_;
285 return ($self->expect_list($op))[0] => 1 if name($op) eq 'return';
287 if (class($op) eq 'LOGOP' and not null $op->first) {
292 ($p, $r) = $self->expect_return($op);
293 return $p => 1 if $r;
296 push @res, ($self->expect_any($op))[0];
298 # If the logop has no else branch, it can also return the *scalar* result of
304 push @res, ($self->expect_any($op))[0];
307 return (add @res) => 0;
310 return $self->expect_list($op);
313 # Stolen from B::Deparse
315 sub padval { $_[0]->{cv}->[0]->PADLIST->ARRAYelt(1)->ARRAYelt($_[1]) }
318 my ($self, $op) = @_;
319 if (class($op) eq 'PADOP') {
320 return $self->padval($op->padix)
321 } else { # class($op) eq "SVOP"
327 my ($self, $op) = @_;
329 # the constant could be in the pad (under useithreads)
330 $sv = $self->padval($op->targ) unless $$sv;
335 my ($self, $op, $exp) = @_;
338 while ($next->flags & OPf_KIDS) {
339 $next = $next->first;
341 while (not null $next) {
343 my ($p, $r) = $self->expect_return($op, $exp);
344 return $p => 1 if $r;
345 $next = $op->sibling;
348 if (name($op) eq 'rv2cv') {
352 my $next = $op->sibling;
353 while (not null $next) {
355 $next = $next->sibling;
358 } while ($op->flags & OPf_KIDS and { map { $_ => 1 } qw/null leave/ }->{$n});
359 return 'list' unless { map { $_ => 1 } qw/gv refgen/ }->{$n};
360 local $self->{sub} = 1;
361 return $self->expect_any($op, $exp);
369 my ($self, $op) = @_;
371 return $self->{sub} ? $self->enter($self->gv_or_padgv($op)->CV) : 1
375 my ($self, $op) = @_;
377 return $self->{sub} ? $self->enter($self->const_sv($op)) : 1
381 my ($self, $op) = @_;
384 while ($op->flags & OPf_KIDS) {
385 my $nop = $op->first;
387 if ($nn eq 'pushmark') {
388 $nop = $nop->sibling;
391 if ($n eq 'rv2cv' and $nn eq 'gv') {
392 return $self->enter($self->gv_or_padgv($nop)->CV);
402 my ($self, $op) = @_;
404 if (class($op) eq 'SVOP' and (my $sv = $self->const_sv($op))) {
407 return $sv->FILL + 1;
408 } elsif ($c eq 'HV') {
409 return 2 * $sv->FILL;
416 sub pp_aslice { $_[0]->expect_any($_[1]->first->sibling) }
419 *pp_hslice = *pp_aslice{CODE};
421 sub pp_lslice { $_[0]->expect_any($_[1]->first) }
424 my ($self, $op) = @_;
427 return (name($op) eq 'const') ? $self->expect_any($op) : 'list';
430 sub pp_aassign { $_[0]->expect_any($_[1]->first) }
432 sub pp_leaveloop { $_[0]->expect_return($_[1]->first->sibling) }
436 An object-oriented module shouldn't export any function, and so does this one.
440 The algorithm may be pessimistic (things seen as C<list> while they are of fixed length) but not optimistic (the opposite, duh).
442 C<wantarray> isn't specialized when encountered in the optree.
448 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).
452 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
454 You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).
458 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.
462 You can find documentation for this module with the perldoc command.
466 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Sub-Nary>.
468 =head1 ACKNOWLEDGEMENTS
470 Thanks to Sebastien Aperghis-Tramoni for helping to name this module.
472 =head1 COPYRIGHT & LICENSE
474 Copyright 2008 Vincent Pit, all rights reserved.
476 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
480 1; # End of Sub::Nary