Power set: Difference between revisions
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version for lists:
<lang ocaml>let subsets xs = List.fold_right (fun x rest -> rest @ List.map (fun ys -> x::ys) rest) xs [[]]</lang>
=={{header|Oz}}==
Oz has a library for finite set constraints. Creating a power set is a trivial application of that:
<lang oz>declare
%% Given a set as a list, returns its powerset (again as a list)
fun {Powerset Set}
proc {Describe Root}
%% Describe sets by lower bound (nil) and upper bound (Set)
Root = {FS.var.bounds nil Set}
%% enumerate all possible sets
{FS.distribute naive [Root]}
end
AllSets = {SearchAll Describe}
in
%% convert to list representation
{Map AllSets FS.reflect.lowerBoundList}
end
in
{Inspect {Powerset [1 2 3 4]}}</lang>
A more convential implementation without finite set constaints:
<lang oz>fun {Powerset2 Set}
case Set of nil then [nil]
[] H|T then
Acc = {Powerset2 T}
in
{Append Acc {Map Acc fun {$ A} H|A end}}
end
end</lang>
=={{header|Perl}}==
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