From: Mart Lubbers <mart@martlubbers.net>
Date: Tue, 3 Mar 2015 11:37:56 +0000 (+0100)
Subject: mooiere powerset
X-Git-Url: https://git.martlubbers.net/?a=commitdiff_plain;h=d21ead92c20299ce914b1e3a7663990f9a3e85f1;p=fp1415.git

mooiere powerset
---

diff --git a/week4/mart/StdSet.dcl b/week4/mart/StdSet.dcl
index 6cad7f1..0c702ca 100644
--- a/week4/mart/StdSet.dcl
+++ b/week4/mart/StdSet.dcl
@@ -22,4 +22,4 @@ product			:: (Set a) (Set b) -> Set (a,b)
 instance zero (Set a)
 instance ==   (Set a) | Eq a
 
-powerSet		:: (Set a)         -> Set (Set a)
+powerSet		:: (Set a)         -> Set (Set a) | Eq a
diff --git a/week4/mart/StdSet.icl b/week4/mart/StdSet.icl
index a14e6ba..ecb2e60 100644
--- a/week4/mart/StdSet.icl
+++ b/week4/mart/StdSet.icl
@@ -48,9 +48,7 @@ where zero = Set []
 instance == (Set a) | Eq a
 where (==) s1 s2 = isSubset s1 s2 && isSubset s2 s1
 
-powerSet	:: (Set a)         -> Set (Set a)
-powerSet (Set a) = Set [(Set x) \\ x <- powerSet2 a]
-where
-	powerSet2	:: [a] -> [[a]]
-	powerSet2 [] = [[]]
-	powerSet2 [e:xs] = (powerSet2 xs) ++ [[e:x] \\ x <- powerSet2 xs]
+powerSet	:: (Set a)         -> Set (Set a) | Eq a
+powerSet (Set []) = Set [(Set [])]
+powerSet (Set [e:xs]) = union (powerSet (Set xs))
+	(Set [union (Set [e]) x \\ x <- fromSet (powerSet (Set xs))])