From: Matt S Trout <mst@shadowcat.co.uk>
Date: Wed, 22 Jun 2016 17:22:36 +0000 (+0000)
Subject: extract backtrack decisions out into steps
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?p=scpubgit%2FDX.git;a=commitdiff_plain;h=c76de01dd23ba8e59821c8587f4e529d31181682

extract backtrack decisions out into steps
---

diff --git a/lib/DX/SearchState.pm b/lib/DX/SearchState.pm
index 99ac3f2..18979e7 100644
--- a/lib/DX/SearchState.pm
+++ b/lib/DX/SearchState.pm
@@ -35,16 +35,8 @@ sub new_for {
 
 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(
-    next_step => DX::Step::Backtrack->new,
-  );
+  return $step->apply_to($self);
 }
 
 sub force_backtrack {
diff --git a/lib/DX/Step/InvokeNextPredicate.pm b/lib/DX/Step/InvokeNextPredicate.pm
index dc9aab1..55bee44 100644
--- a/lib/DX/Step/InvokeNextPredicate.pm
+++ b/lib/DX/Step/InvokeNextPredicate.pm
@@ -12,7 +12,7 @@ sub apply_to {
   if (my $step = $self->proposition->resolve_for($hyp->scope)) {
     return $ss->but(next_step => $step);
   }
-  return undef;
+  return $ss->but(next_step => DX::Step::Backtrack->new);
 }
 
 1;
diff --git a/lib/DX/Step/Normal.pm b/lib/DX/Step/Normal.pm
index 2ec93aa..e314088 100644
--- a/lib/DX/Step/Normal.pm
+++ b/lib/DX/Step/Normal.pm
@@ -30,7 +30,7 @@ sub apply_to {
   trace 'step.apply.old_hyp '.$self => $old_hyp;
   trace 'step.apply.actions '.$self => $self->actions;
   my $new_hyp = $self->_apply_to_hyp($old_hyp);
-  return (undef, $self->alternative_step) unless $new_hyp;
+  return $ss->but(next_step => DX::Step::Backtrack->new) unless $new_hyp;
   trace 'step.apply.new_hyp '.$self => $new_hyp;
   my $ns = DX::Step::InvokeNextPredicate->new(
     proposition => $ss->next_proposition($new_hyp)