From: Matt S Trout <mst@shadowcat.co.uk>
Date: Mon, 16 Apr 2018 02:25:14 +0000 (+0000)
Subject: skip backtracking rspaces with no alternatives left
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=b63c427e5f7bf56fce5308a970a7402a4d62e0d4;p=scpubgit%2FDX.git

skip backtracking rspaces with no alternatives left
---

diff --git a/fragment.output/btdemo b/fragment.output/btdemo
index c75951e..f42caa6 100644
--- a/fragment.output/btdemo
+++ b/fragment.output/btdemo
@@ -244,13 +244,6 @@ recheck eq ?X {{ a 1 b 2 c 3 }} {
 }
 backtrack
 remaining resolution_space {
-    proposition member_at Y ?YKey ?YValue
-    geometry_depends_on { INDICES_OF 0.Y; TYPE_OF 0.YKey; TYPE_OF 0.YValue }
-    aperture { VALUE_SET 0.YKey; VALUE_SET 0.YValue }
-    members {  }
-}
-backtrack
-remaining resolution_space {
     proposition member_at X ?XKey ?XValue
     geometry_depends_on { INDICES_OF 0.X; TYPE_OF 0.XKey; TYPE_OF 0.XValue }
     aperture { VALUE_SET 0.XKey; VALUE_SET 0.XValue }
@@ -340,13 +333,6 @@ recheck eq ?Y {{ d 1 e 2 f 3 }} {
 }
 backtrack
 remaining resolution_space {
-    proposition eq XValue 2
-    geometry_depends_on { CONTENTS_OF 0.XValue }
-    aperture { VALUE_SET 0.XValue; VALUE_SET 0.X.b }
-    members {  }
-}
-backtrack
-remaining resolution_space {
     proposition member_at Y ?YKey ?YValue
     geometry_depends_on { INDICES_OF 0.Y; TYPE_OF 0.YKey; TYPE_OF 0.YValue }
     aperture { VALUE_SET 0.YKey; VALUE_SET 0.YValue }
@@ -448,20 +434,6 @@ recheck eq ?Y {{ d 1 e 2 f 3 }} {
 }
 backtrack
 remaining resolution_space {
-    proposition eq XValue 2
-    geometry_depends_on { CONTENTS_OF 0.XValue }
-    aperture { VALUE_SET 0.XValue; VALUE_SET 0.X.b }
-    members {  }
-}
-backtrack
-remaining resolution_space {
-    proposition member_at Y ?YKey ?YValue
-    geometry_depends_on { INDICES_OF 0.Y; TYPE_OF 0.YKey; TYPE_OF 0.YValue }
-    aperture { VALUE_SET 0.YKey; VALUE_SET 0.YValue }
-    members {  }
-}
-backtrack
-remaining resolution_space {
     proposition member_at X ?XKey ?XValue
     geometry_depends_on { INDICES_OF 0.X; TYPE_OF 0.XKey; TYPE_OF 0.XValue }
     aperture { VALUE_SET 0.XKey; VALUE_SET 0.XValue }
@@ -650,34 +622,6 @@ recheck eq ?X {{ a 1 b 2 c 3 }} {
     fail_recheck
 }
 backtrack
-remaining resolution_space {
-    proposition member_at Y ?YKey ?YValue
-    geometry_depends_on { INDICES_OF 0.Y; TYPE_OF 0.YKey; TYPE_OF 0.YValue }
-    aperture { VALUE_SET 0.YKey; VALUE_SET 0.YValue }
-    members {  }
-}
-backtrack
-remaining resolution_space {
-    proposition member_at X ?XKey ?XValue
-    geometry_depends_on { INDICES_OF 0.X; TYPE_OF 0.XKey; TYPE_OF 0.XValue }
-    aperture { VALUE_SET 0.XKey; VALUE_SET 0.XValue }
-    members {  }
-}
-backtrack
-remaining resolution_space {
-    proposition eq ?Y {{ d 1 e 2 f 3 }}
-    geometry_depends_on { CONTENTS_OF 0.Y }
-    aperture { VALUE_SET 0.Y }
-    members {  }
-}
-backtrack
-remaining resolution_space {
-    proposition eq ?X {{ a 1 b 2 c 3 }}
-    geometry_depends_on { CONTENTS_OF 0.X }
-    aperture { VALUE_SET 0.X }
-    members {  }
-}
-backtrack
 {{
     X {{ a 1 b 2 c 3 }}
     XKey 'b'
diff --git a/lib/DX/Step/Backtrack.pm b/lib/DX/Step/Backtrack.pm
index 865073a..9a92677 100644
--- a/lib/DX/Step/Backtrack.pm
+++ b/lib/DX/Step/Backtrack.pm
@@ -11,6 +11,7 @@ sub apply_to {
   trace backtrack => [ statement => [ [ symbol => 'backtrack' ] ] ];
   foreach my $adj (@{$ss->decisions_taken}) {
     my ($rspace_was, $ss_was) = @$adj;
+    next unless @{$rspace_was->remaining_resolution_space->members};
     trace rspace => [ statement => [
       [ symbol => 'remaining' ],
       @{$rspace_was->remaining_resolution_space->for_deparse->[1]}