euc2003

[Bjorn Gustavsson]

It can handle recursive generators if you limit the size of the generated
sets. At the end of this email, I've attached a module that does some
tests on the gb_sets module. 

/Bjorn

Luke Gorrie <luke@REDACTED> writes:

> The online version seems a bit older than the one presented, it
> doesn't handle recursively defined generators (as the 'sets' one
> is). I'll steal the latest code for Jungerl when John gets a chance to
> put it online, and until then there's a simpler example in there.
> 

-- 
Björn Gustavsson            Ericsson Utvecklings AB
bjorn@REDACTED      ÄT2/UAB/F/P
			    BOX 1505
+46 8 727 56 87 	    125 25 Älvsjö

-module(gb_sets_check).
-compile(export_all).

-include("quickcheck.hrl").

t() ->
    qc:quickcheck(prop_union_commutes()),
    qc:quickcheck(prop_intersection_commutes()),
    qc:quickcheck(prop_subset()),
    qc:quickcheck(prop_empty()),
    qc:quickcheck(prop_not_empty()),

    %% Intentionally failing property.
    qc:quickcheck(prop_difference_commutes()),

    ok.

prop_union_commutes() ->
    ?FORALL(X,gb_set(),
	?FORALL(Y,gb_set(),
	equal(gb_sets:union(X, Y), gb_sets:union(Y, X)))).

prop_intersection_commutes() ->
    ?FORALL(X,gb_set(),
	?FORALL(Y,gb_set(),
	equal(gb_sets:intersection(X, Y), gb_sets:intersection(Y, X)))).

prop_difference_commutes() ->
    ?FORALL(X,gb_set(),
	?FORALL(Y,gb_set(),
	equal(gb_sets:difference(X, Y), gb_sets:difference(Y, X)))).

prop_subset() ->
    ?FORALL(X,gb_set(),
	?FORALL(Y,gb_set(),
	begin S = gb_sets:union(X, Y),
	gb_sets:is_subset(X, S) andalso gb_sets:is_subset(Y, S) end)).

prop_empty() ->
    ?FORALL(X,gb_set(),
	?IMPLIES(gb_sets:size(X) == 0, gb_sets:is_empty(X))).

prop_not_empty() ->
    ?FORALL(X,gb_set(),
	?IMPLIES(gb_sets:size(X) /= 0, not gb_sets:is_empty(X))).

gb_set() ->
    ?SIZED(N, resize(min(50, N),
	frequency(
	[{6,?LET(L, list(int()),
	return({'@',gb_sets,from_list,[L]}))},
	{6,?LET(L, list(int()),
	return({'@',gb_sets,from_ordset,[{'@',ordsets,from_list,[L]}]}))},
	{6,?LET(S,gb_set(),?LET(E,int(),
 	return({'@',gb_sets,add,[E,S]})))},
	{2,return({'@',gb_sets,empty,[]})},
	{2,?LET(E,int(),
	return({'@',gb_sets,singleton,[E]}))},
	{1,?LET(P,function(bool()),?LET(S,gb_set(),
	return({'@',gb_sets,filter,[P,S]})))}
       ]))).
    
equal(X, Y) ->
    gb_sets:to_list(X) =:= gb_sets:to_list(Y).

min(A, B) when A < B -> A;
min(_, B) -> B.