1 files changed, 52 insertions, 0 deletions
diff --git a/ghc/compiler/tests/deSugar/ds020.hs b/ghc/compiler/tests/deSugar/ds020.hs
new file mode 100644
index 0000000000..ac6ea8dd4b
--- /dev/null
+++ b/ghc/compiler/tests/deSugar/ds020.hs
@@ -0,0 +1,52 @@
+--!!! ds020 -- lazy patterns (in detail)
+--
+module Test where
+
+a ~([],[],[])    = []
+a ~(~[],~[],~[]) = []
+
+b ~(x:xs:ys)      = []
+b ~(~x: ~xs: ~ys) = []
+
+c ~x ~ _ ~11111 ~3.14159265 = x
+
+d 11	    = 4
+d 12	    = 3
+d ~(n+4)    = 2
+d ~(n+43)   = 1
+d ~(n+999)  = 0
+
+f ~(x@[]) = []
+f x@(~[]) = []
+
+g ~(~(~(~([])))) = []
+
+-- pattern bindings (implicitly lazy)
+
+([],[],[])    = ([],[],[])
+(~[],~[],~[]) = ([],[],[])
+
+(x1: xs1: ys1) = []
+(~x: ~xs: ~ys) = []
+
+(x2 : xs2: ys2) | eq2  = []
+	        | eq3  = [x2]
+		| eq4  = [x2]
+		| True = []
+		where
+		  eq2 = (2::Int) == (4::Int)
+		  eq3 = (3::Int) == (3::Int)
+		  eq4 = (4::Int) == (2::Int)
+
+(x3,y3) | x3 >  3 = (4, 5)
+        | x3 <= 3 = (2, 3)
+-- above: x & y should both be \bottom.
+
+(x4,(y4,(z4,a4))) | eq2  = ('a',('a',('a','a')))
+	          | eq3  = ('b',('b',('b','b')))
+	          | eq4  = ('c',('c',('c','c')))
+	          | True = ('d',('d',('d','d')))
+	          where
+		     eq2 = (2::Int) == (4::Int)
+		     eq3 = (3::Int) == (3::Int)
+		     eq4 = (4::Int) == (2::Int)