mark propositionless search states as solutions

[scpubgit/DX.git] / lib / DX / SearchState.pm

diff --git a/lib/DX/SearchState.pm b/lib/DX/SearchState.pm
index 9562373..1548f11 100644 (file)
--- a/lib/DX/SearchState.pm
+++ b/lib/DX/SearchState.pm
@@ -1,6 +1,7 @@
 package DX::SearchState;
 
 use Types::Standard qw(Maybe);
+use DX::Step::Backtrack;
 use DX::Step::InvokeNextPredicate;
 use DX::Class;
 
@@ -12,6 +13,8 @@ has propositions => (is => 'ro', isa => PropositionSequence, required => 1);
 
 has alternatives => (is => 'ro', isa => AlternativeList, required => 1);
 
+has is_solution_state => (is => 'ro', required => 1);
+
 sub next_proposition {
   my ($self, $hyp) = @_;
   $hyp ||= $self->current_hypothesis;
@@ -25,27 +28,23 @@ sub new_for {
   $class->new(
     current_hypothesis => $hyp,
     alternatives => [],
-    next_step => DX::Step::InvokeNextPredicate->new(
-      proposition => $props->members->[0],
-    ),
     propositions => $props,
+    (@{$props->members}
+      ? (
+          next_step => DX::Step::InvokeNextPredicate->new(
+            proposition => $props->members->[0],
+          ),
+          is_solution_state => 0,
+        )
+      : ( is_solution_state => 1 )
+    ),
   );
 }
 
 sub with_one_step {
   my ($self) = @_;
-  my $hyp = $self->current_hypothesis;
   return undef unless my $step = $self->next_step;
-  my ($new_ss) = $step->apply_to($self);
-  return $new_ss if $new_ss;
-  my ($first_alt, @rest_alt) = @{$self->alternatives};
-  return undef unless $first_alt;
-  trace 'search.backtrack.rewind_to' => $first_alt->[1];
-  return $self->but(
-    current_hypothesis => $first_alt->[0],
-    alternatives => \@rest_alt,
-    next_step => $first_alt->[1],
-  );
+  return $step->apply_to($self);
 }
 
 sub force_backtrack {
@@ -53,12 +52,9 @@ sub force_backtrack {
   my ($first_alt, @rest_alt) = @{$self->alternatives};
   return undef unless $first_alt;
   trace 'search.backtrack.forced' => $first_alt->[0];
-  return ref($self)->new(
-    current_hypothesis => $first_alt->[0],
-    next_step => $first_alt->[1],
-    alternatives => \@rest_alt,
-    propositions => $self->propositions,
-  );
+  return $self->but(
+    next_step => DX::Step::Backtrack->new,
+  )->with_one_step;
 }
 
 1;