create explicit on_exhaustion_step attribute

diff --git a/lib/DX/SearchState.pm b/lib/DX/SearchState.pm
index 1548f11..a19a416 100644 (file)
--- a/lib/DX/SearchState.pm
+++ b/lib/DX/SearchState.pm
@@ -15,6 +15,8 @@ has alternatives => (is => 'ro', isa => AlternativeList, required => 1);
 
 has is_solution_state => (is => 'ro', required => 1);
 
+has on_exhaustion_step => (is => 'ro', required => 1);
+
 sub next_proposition {
   my ($self, $hyp) = @_;
   $hyp ||= $self->current_hypothesis;
@@ -38,6 +40,7 @@ sub new_for {
         )
       : ( is_solution_state => 1 )
     ),
+    on_exhaustion_step => undef,
   );
 }
 

diff --git a/lib/DX/Step/Backtrack.pm b/lib/DX/Step/Backtrack.pm
index 8e3b5d8..3306fc3 100644 (file)
--- a/lib/DX/Step/Backtrack.pm
+++ b/lib/DX/Step/Backtrack.pm
@@ -7,7 +7,7 @@ with 'DX::Role::Step';
 sub apply_to {
   my ($self, $ss) = @_;
   my ($first_alt, @rest_alt) = @{$ss->alternatives};
-  return $ss->but(next_step => undef) unless $first_alt;
+  return $ss->but(next_step => $ss->on_exhaustion_step) unless $first_alt;
   trace 'search.backtrack.rewind_to' => $first_alt->[1];
   return $ss->but(
     current_hypothesis => $first_alt->[0],