Make Random for a finite collection take an optional source

This requires moving the function to random.gi, as we want to use InstallMethodWithRandomSource.
gap-system · Mar 6, 2018 · 4add79c · 4add79c
1 parent 40bc9ac
commit 4add79c
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/lib/coll.gi b/lib/coll.gi
@@ -264,12 +264,10 @@ InstallGlobalFunction( RandomList, function(args...)
 
  return list[Random(source, 1, Length(list))];
 end );
-InstallMethod( Random, "for a (finite) collection",
- [ IsCollection and IsFinite ],
- C -> RandomList( Enumerator( C ) ) );
 
-RedispatchOnCondition(Random,true,[IsCollection],[IsFinite],0);
 
+RedispatchOnCondition(Random,true,[IsCollection],[IsFinite],0);
+RedispatchOnCondition(Random,true,[IsRandomSource,IsCollection],[IsFinite],0);
 
 #############################################################################
 ##

diff --git a/lib/random.gi b/lib/random.gi
@@ -311,3 +311,9 @@ end );
  InstallGlobalFunction("InstallMethodWithRandomSource", func(InstallMethod));
  InstallGlobalFunction("InstallOtherMethodWithRandomSource", func(InstallOtherMethod));
 end)();
+
+# This method must rank below Random(SomeRandomSource, IsList)
+# for any random source SomeRandomSource, to avoid an infinite loop.
+InstallMethodWithRandomSource( Random, "for a random source and a (finite) collection",
+ [ IsRandomSource, IsCollection and IsFinite ], -8,
+ {rs, C} -> RandomList(rs, Enumerator( C ) ) );