add some more transposition logic

diff --git a/lib/Text/Tradition/Collation/RelationshipStore.pm b/lib/Text/Tradition/Collation/RelationshipStore.pm
index ddad4db..b6e71cb 100644 (file)
--- a/lib/Text/Tradition/Collation/RelationshipStore.pm
+++ b/lib/Text/Tradition/Collation/RelationshipStore.pm
@@ -461,9 +461,30 @@ sub relationship_valid {
                                return ( 1, "ok" ) if $rel eq 'repetition';
                        }
                }
-               return $rel eq 'transposition' ? ( 1, "ok" )
-                       : ( 0, "Readings occur only in distinct witnesses" );
-       } else {
+               return ( 0, "Readings occur only in distinct witnesses" )
+                       if $rel eq 'repetition';
+       } 
+       if ( $rel eq 'transposition' ) {
+               # We also need to check both that the readings occur in distinct
+               # witnesses, and that they are not in the same place. That is,
+               # proposing to link them should cause a witness loop.
+               my $map = {};
+               my( $startrank, $endrank );
+               if( $c->end->has_rank ) {
+                       my $cpred = $c->common_predecessor( $source, $target );
+                       my $csucc = $c->common_successor( $source, $target );
+                       $startrank = $cpred->rank;
+                       $endrank = $csucc->rank;
+               }
+               my $eqgraph = $c->equivalence_graph( $map, $startrank, $endrank, 
+                       $source, $target );
+               if( $eqgraph->has_a_cycle ) {
+                       return ( 1, "ok" );
+               } else {
+                       return ( 0, "Readings appear to be colocated, not transposed" );
+               }
+               
+       } elsif( $rel ne 'repetition' ) {
                # Check that linking the source and target in a relationship won't lead
                # to a path loop for any witness. 
                # First, drop/stash any collations that might interfere