lib: add operation DirectProductFamily

This declares the new operation DirectProductFamily, installs a method for it. This makes the method installed for UnderlyingRelation easier to read.
gap-system · May 17, 2019 · 2c4928e · 2c4928e
1 parent f30c1e4
commit 2c4928e
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Showing 3 changed files with 27 additions and 6 deletions.
diff --git a/lib/mapping.gi b/lib/mapping.gi
@@ -1259,12 +1259,11 @@ InstallMethod( UnderlyingRelation,
  true,
  [ IsGeneralMapping ], 0,
  function( map )
- local rel;
- rel:= Objectify( NewType( CollectionsFamily(
- DirectProductElementsFamily( [ ElementsFamily( FamilyObj( Source( map ) ) ),
- ElementsFamily( FamilyObj( Range( map ) ) ) ] ) ),
- IsDomain and IsAttributeStoringRep ),
- rec() );
+ local type, rel;
+ type:= NewType( DirectProductFamily( [ FamilyObj( Source( map ) ),
+ FamilyObj( Range( map ) ) ] ),
+ IsDomain and IsAttributeStoringRep );
+ rel:= Objectify( type, rec() );
  SetUnderlyingGeneralMapping( rel, map );
  return rel;
  end );

diff --git a/lib/tuples.gd b/lib/tuples.gd
@@ -178,3 +178,9 @@ direct product elements families" );
 DeclareOperation( "DirectProductElement", [ IsList ]);
 DeclareOperation( "DirectProductElementNC",
  [ IsDirectProductElementFamily, IsList ]);
+
+
+#############################################################################
+##
+##
+DeclareOperation( "DirectProductFamily", [ IsDenseList ] );
diff --git a/lib/tuples.gi b/lib/tuples.gi
@@ -506,3 +506,19 @@ InstallOtherMethod( \*,
  fi;
  return DirectProductElement( List( dpelm, entry -> nonlist * entry ) );
  end );
+
+
+#############################################################################
+##
+##
+InstallMethod( DirectProductFamily,
+ "for a collection (of families)",
+ fam -> fam = CollectionsFamily(FamilyOfFamilies),
+ [ IsDenseList ],
+ function( args )
+ return CollectionsFamily(
+ DirectProductElementsFamily(
+ List( args, x -> ElementsFamily( x ) )
+ )
+ );
+ end );