package Sub::Nary;
use 5.008001;
use strict;
use warnings;
use Carp qw/croak/;
use B qw/class ppname svref_2object OPf_KIDS/;
=head1 NAME
Sub::Nary - Try to count how many elements a subroutine can return in list context.
=head1 VERSION
Version 0.03
=cut
our $VERSION;
BEGIN {
$VERSION = '0.03';
}
=head1 SYNOPSIS
use Sub::Nary;
my $sn = Sub::Nary->new();
my $r = $sn->nary(\&hlagh);
=head1 DESCRIPTION
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).
=head1 METHODS
=head2 C<new>
The usual constructor. Currently takes no argument.
=head2 C<nary $coderef>
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
{ 1 => 0.2, 2 => 0.4, 4 => 0.3, list => 0.1 }
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.
=head2 C<flush>
Flushes the L<Sub::Nary> object cache. Returns the object itself.
=head1 PROBABILITY OF RETURN
The probability is computed as such :
=over 4
=item * When branching, each branch is considered equally possible.
For example, the subroutine
sub simple {
if (rand < 0.1) {
return 1;
} else {
return 2, 3;
}
}
is seen returning one or two arguments each with probability C<1/2>.
As for
sub hlagh {
my $x = rand;
if ($x < 0.1) {
return 1, 2, 3;
} elsif ($x > 0.9) {
return 4, 5;
}
}
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>.
=item * The total probability law for a given returning point is the convolution product of the probabilities of its list elements.
As such,
sub notsosimple {
return 1, simple(), 2
}
returns C<3> or C<4> arguments with probability C<1/2> ; and
sub double {
return simple(), simple()
}
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.
=item * If a core function may return different numbers of scalars, each kind is considered equally possible.
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 } >>.
=item * The C<list> state is absorbing in regard of all the other ones.
This is just a pedantic way to say that "list + fixed length = list".
That's why
sub listy {
return 1, simple(), @_
}
is considered as always returning an unbounded list.
Also, the convolution law does not behave the same when C<list> elements are involved : in the following example,
sub oneorlist {
if (rand < 0.1) {
return 1
} else {
return @_
}
}
sub composed {
return oneorlist(), oneorlist()
}
C<composed> returns C<2> scalars with probability C<1/2 * 1/2 = 1/4> and a C<list> with probability C<3/4>.
=back
=cut
BEGIN {
require XSLoader;
XSLoader::load(__PACKAGE__, $VERSION);
}
sub _check_self {
croak 'First argument isn\'t a valid ' . __PACKAGE__ . ' object'
unless ref $_[0] and $_[0]->isa(__PACKAGE__);
}
sub new {
my $class = shift;
$class = ref($class) || $class || __PACKAGE__;
bless { cache => { } }, $class;
}
sub flush {
my $self = shift;
_check_self($self);
$self->{cache} = { };
$self;
}
sub nary {
my $self = shift;
my $sub = shift;
$self->{cv} = [ ];
return ($self->enter(svref_2object($sub)))[1];
}
sub name ($) {
local $SIG{__DIE__} = \&Carp::confess;
my $n = $_[0]->name;
$n eq 'null' ? substr(ppname($_[0]->targ), 3) : $n
}
sub power {
my ($p, $n, $c) = @_;
return unless defined $p;
return { 0 => $c } unless $n;
if ($n eq 'list') {
my $z = delete $p->{0};
return { 'list' => $c } unless $z;
return { 0 => $c } if $z == 1;
return { 0 => $c * $z, list => $c * (1 - $z) };
}
my $r = combine map { { %$p } } 1 .. $n;
$r->{$_} *= $c for keys %$r;
return $r;
}
my %ops;
$ops{$_} = 1 for scalops;
$ops{$_} = 0 for qw/stub nextstate pushmark iter unstack/;
$ops{$_} = 1 for qw/padsv/;
$ops{$_} = 'list' for qw/padav/;
$ops{$_} = 'list' for qw/padhv rv2hv/;
$ops{$_} = 'list' for qw/padany/;
$ops{$_} = 'list' for qw/match entereval readline/;
$ops{each} = { 0 => 0.5, 2 => 0.5 };
$ops{stat} = { 0 => 0.5, 13 => 0.5 };
$ops{caller} = sub { my @a = caller 0; scalar @a }->();
$ops{localtime} = do { my @a = localtime; scalar @a };
$ops{gmtime} = do { my @a = gmtime; scalar @a };
$ops{$_} = { 0 => 0.5, 10 => 0.5 } for map "gpw$_", qw/nam uid ent/;
$ops{$_} = { 0 => 0.5, 4 => 0.5 } for map "ggr$_", qw/nam gid ent/;
$ops{$_} = 'list' for qw/ghbyname ghbyaddr ghostent/;
$ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gnbyname gnbyaddr gnetent/;
$ops{$_} = { 0 => 0.5, 3 => 0.5 } for qw/gpbyname gpbynumber gprotoent/;
$ops{$_} = { 0 => 0.5, 4 => 0.5 } for qw/gsbyname gsbyport gservent/;
sub enter {
my ($self, $cv) = @_;
return undef, 'list' if class($cv) ne 'CV';
my $op = $cv->ROOT;
my $tag = tag($op);
return undef, { %{$self->{cache}->{$tag}} } if exists $self->{cache}->{$tag};
# Anything can happen with recursion
for (@{$self->{cv}}) {
return undef, 'list' if $tag == tag($_->ROOT);
}
unshift @{$self->{cv}}, $cv;
my $r = add $self->inspect($op->first);
shift @{$self->{cv}};
$r = { $r => 1 } unless ref $r;
$self->{cache}->{$tag} = { %$r };
return undef, $r;
}
sub inspect {
my ($self, $op) = @_;
my $n = name($op);
return add($self->inspect_kids($op)), undef if $n eq 'return';
my $meth = $self->can('pp_' . $n);
return $self->$meth($op) if $meth;
if (exists $ops{$n}) {
my $l = $ops{$n};
$l = { %$l } if ref $l;
return undef, $l;
}
if (class($op) eq 'LOGOP' and not null $op->first) {
my @res;
my $op = $op->first;
my ($r1, $l1) = $self->inspect($op);
return $r1, $l1 if defined $r1 and zero $l1;
my $c = count $l1;
$op = $op->sibling;
my ($r2, $l2) = $self->inspect($op);
$op = $op->sibling;
my ($r3, $l3);
if (null $op) {
# If the logop has no else branch, it can also return the *scalar* result of
# the conditional
$l3 = { 1 => 1 };
} else {
($r3, $l3) = $self->inspect($op);
}
my $r = add $r1, scale $c / 2, add $r2, $r3;
my $l = scale $c / 2, add $l2, $l3;
return $r, $l
}
return $self->inspect_kids($op);
}
sub inspect_kids {
my ($self, $op) = @_;
return undef, 0 unless $op->flags & OPf_KIDS;
$op = $op->first;
return undef, 0 if null $op;
if (name($op) eq 'pushmark') {
$op = $op->sibling;
return undef, 0 if null $op;
}
my ($r, @l);
my $c = 1;
for (; not null $op; $op = $op->sibling) {
my $n = name($op);
if ($n eq 'nextstate') {
@l = ();
next;
}
if ($n eq 'lineseq') {
@l = ();
$op = $op->first;
redo;
}
my ($rc, $lc) = $self->inspect($op);
$c = 1 - count $r;
$r = add $r, scale $c, $rc if defined $rc;
if (not defined $lc) {
@l = ();
last;
}
push @l, scale $c, $lc;
}
my $l = scale +(1 - count $r), normalize combine @l;
return $r, $l;
}
# Stolen from B::Deparse
sub padval { $_[0]->{cv}->[0]->PADLIST->ARRAYelt(1)->ARRAYelt($_[1]) }
sub gv_or_padgv {
my ($self, $op) = @_;
if (class($op) eq 'PADOP') {
return $self->padval($op->padix)
} else { # class($op) eq "SVOP"
return $op->gv;
}
}
sub const_sv {
my ($self, $op) = @_;
my $sv = $op->sv;
# the constant could be in the pad (under useithreads)
$sv = $self->padval($op->targ) unless $$sv;
return $sv;
}
sub pp_entersub {
my ($self, $op) = @_;
$op = $op->first while $op->flags & OPf_KIDS;
return undef, 0 if null $op;
if (name($op) eq 'pushmark') {
$op = $op->sibling;
return undef, 0 if null $op;
}
my $r;
my $c = 1;
for (; not null $op->sibling; $op = $op->sibling) {
my ($rc, $lc) = $self->inspect($op);
return $rc, $lc if defined $rc and not defined $lc;
$r = add $r, scale $c, $rc;
$c *= count $lc;
}
if (name($op) eq 'rv2cv') {
my $n;
do {
$op = $op->first;
my $next = $op->sibling;
while (not null $next) {
$op = $next;
$next = $next->sibling;
}
$n = name($op)
} while ($op->flags & OPf_KIDS and { map { $_ => 1 } qw/null leave/ }->{$n});
return 'list', undef unless { map { $_ => 1 } qw/gv refgen/ }->{$n};
local $self->{sub} = 1;
my ($rc, $lc) = $self->inspect($op);
return $r, scale $c, $lc;
} else {
# Method call ?
return $r, { 'list' => $c };
}
}
sub pp_gv {
my ($self, $op) = @_;
return $self->{sub} ? $self->enter($self->gv_or_padgv($op)->CV) : (undef, 1)
}
sub pp_anoncode {
my ($self, $op) = @_;
return $self->{sub} ? $self->enter($self->const_sv($op)) : (undef, 1)
}
sub pp_goto {
my ($self, $op) = @_;
my $n = name($op);
while ($op->flags & OPf_KIDS) {
my $nop = $op->first;
my $nn = name($nop);
if ($nn eq 'pushmark') {
$nop = $nop->sibling;
$nn = name($nop);
}
if ($n eq 'rv2cv' and $nn eq 'gv') {
return $self->enter($self->gv_or_padgv($nop)->CV);
}
$op = $nop;
$n = $nn;
}
return undef, 'list';
}
sub pp_const {
my ($self, $op) = @_;
return undef, 0 unless $op->isa('B::SVOP');
my $sv = $self->const_sv($op);
my $n = 1;
my $c = class($sv);
if ($c eq 'AV') {
$n = $sv->FILL + 1
} elsif ($c eq 'HV') {
$n = 2 * $sv->KEYS
}
return undef, $n
}
sub pp_aslice { $_[0]->inspect($_[1]->first->sibling) }
sub pp_hslice;
*pp_hslice = *pp_aslice{CODE};
sub pp_lslice { $_[0]->inspect($_[1]->first) }
sub pp_rv2av {
my ($self, $op) = @_;
$op = $op->first;
if (name($op) eq 'gv') {
return undef, { list => 1 };
}
$self->inspect($op);
}
sub pp_aassign {
my ($self, $op) = @_;
$op = $op->first;
# Can't assign to return
my $l = ($self->inspect($op->sibling))[1];
return undef, $l if not exists $l->{list};
$self->inspect($op);
}
sub pp_leaveloop {
my ($self, $op) = @_;
$op = $op->first;
my ($r1, $l1);
my $for;
if (name($op) eq 'enteriter') { # for loop ?
$for = 1;
($r1, $l1) = $self->inspect($op);
return $r1, $l1 if defined $r1 and zero $l1;
}
$op = $op->sibling;
my ($r2, $l2);
if (name($op->first) eq 'and') {
($r2, $l2) = $self->inspect($op->first->first);
return $r2, $l2 if defined $r2 and zero $l2;
my $c = count $l2;
return { list => 1 }, undef if !$for and defined $r2;
my ($r3, $l3) = $self->inspect($op->first->first->sibling);
return { list => 1 }, undef if defined $r3 and defined $l3;
$r2 = add $r2, scale $c, $r3;
} else {
($r2, $l2) = $self->inspect($op);
return { list => 1 }, undef if defined $r2 and defined $l2;
}
my $r = (defined $r1) ? add $r1, scale +(1 - count $r1), $r2
: $r2;
my $c = 1 - count $r;
return $r, $c ? { 0 => $c } : undef;
}
sub pp_flip {
my ($self, $op) = @_;
$op = $op->first;
return $self->inspect($op) if name($op) ne 'range';
my ($r, $l);
my $begin = $op->first;
if (name($begin) eq 'const') {
my $end = $begin->sibling;
if (name($end) eq 'const') {
$begin = $self->const_sv($begin);
$end = $self->const_sv($end);
{
no warnings 'numeric';
$begin = int ${$begin->object_2svref};
$end = int ${$end->object_2svref};
}
return undef, $end - $begin + 1;
} else {
($r, $l) = $self->inspect($end);
}
} else {
($r, $l) = $self->inspect($begin);
}
my $c = 1 - count $r;
return $r, $c ? { 'list' => $c } : undef
}
sub pp_grepwhile {
my ($self, $op) = @_;
$op = $op->first;
return $self->inspect($op) if name($op) ne 'grepstart';
$op = $op->first->sibling;
my ($r2, $l2) = $self->inspect($op->sibling);
return $r2, $l2 if defined $r2 and zero $l2;
my $c2 = count $l2; # First one to happen
my ($r1, $l1) = $self->inspect($op);
return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
and not zero $l2;
my $c1 = count $l1;
$l2 = { $l2 => 1 } unless ref $l2;
my $r = add $r2,
scale $c2,
add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
my $c = 1 - count $r;
return $r, $c ? { ((zero $l2) ? 0 : 'list') => $c } : undef;
}
sub pp_mapwhile {
my ($self, $op) = @_;
$op = $op->first;
return $self->inspect($op) if name($op) ne 'mapstart';
$op = $op->first->sibling;
my ($r2, $l2) = $self->inspect($op->sibling);
return $r2, $l2 if defined $r2 and zero $l2;
my $c2 = count $l2; # First one to happen
my ($r1, $l1) = $self->inspect($op);
return (add $r2, scale $c2, $r1), undef if defined $r1 and zero $l1
and not zero $l2;
my $c1 = count $l1;
$l2 = { $l2 => 1 } unless ref $l2;
my $r = add $r2,
scale $c2,
add map { scale $l2->{$_}, cumulate $r1, $_, $c1 } keys %$l2;
my $c = 1 - count $r;
my $l = scale $c, normalize add map { power $l1, $_, $l2->{$_} } keys %$l2;
return $r, $l;
}
=head1 EXPORT
An object-oriented module shouldn't export any function, and so does this one.
=head1 CAVEATS
The algorithm may be pessimistic (things seen as C<list> while they are of fixed length) but not optimistic (the opposite, duh).
C<wantarray> isn't specialized when encountered in the optree.
=head1 DEPENDENCIES
L<perl> 5.8.1.
L<Carp> (standard since perl 5), L<B> (since perl 5.005) and L<XSLoader> (since perl 5.006).
=head1 AUTHOR
Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).
=head1 BUGS
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.
=head1 SUPPORT
You can find documentation for this module with the perldoc command.
perldoc Sub::Nary
Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Sub-Nary>.
=head1 ACKNOWLEDGEMENTS
Thanks to Sebastien Aperghis-Tramoni for helping to name this module.
=head1 COPYRIGHT & LICENSE
Copyright 2008 Vincent Pit, all rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
=cut
1; # End of Sub::Nary