stdlib: Add list functions

share/wake/lib/core/list.wake

@@ -900,26 +900,25 @@ export def groupBy (cmpFn: a => a => Order) (list: List a): List (List a) =
 #
 # Examples:
 # ```
-#   intersect icmp (seq 3) (seq 4) = (0, 1, 2, Nil)
-#   intersect icmp (seq 3) (seq 3) = (0, 1, 2, Nil)
-#   intersect icmp (seq 3) (4, 2, 0, Nil) = (0, 2, Nil)
-#   intersect scmp ("", "bar", "bat", Nil) ("", "foo", "bat", Nil) = ("", "bat", Nil)
+#   intersect icmp (seq 3) (seq 4) = 0, 1, 2, Nil
+#   intersect icmp (seq 3) (seq 3) = 0, 1, 2, Nil
+#   intersect icmp (seq 3) (4, 2, 0, Nil) = 0, 2, Nil
+#   intersect scmp ("", "bar", "bat", Nil) ("", "foo", "bat", Nil) = "", "bat", Nil
 # ```
 export def intersect (cmpFn: a => a => Order) (lhs: List a) (rhs: List a): List a =
-    def lhsSort = sortBy cmpFn lhs
-    def rhsSort = sortBy cmpFn rhs
-
-    match lhsSort rhsSort
+    def intersectImp cmpFn lhsSort rhsSort = match lhsSort rhsSort
         # If either list is exhuasted then no more matches are possible
         Nil _ -> Nil
         _ Nil -> Nil
         (lh, lt) (rh, rt) -> match (cmpFn lh rh)
             # lh is smaller so drop it
-            LT -> intersect cmpFn lt (rh, rt)
+            LT -> intersectImp cmpFn lt (rh, rt)
             # rh is smaller so drop it
-            GT -> intersect cmpFn (lh, lt) rt
+            GT -> intersectImp cmpFn (lh, lt) rt
             # equal, grab and continue
-            EQ -> lh, (intersect cmpFn lt rt)
+            EQ -> lh, (intersectImp cmpFn lt rt)
+
+    intersectImp cmpFn (sortBy cmpFn lhs) (sortBy cmpFn rhs)
 
 # Returns a Boolean determining if all items in lhs are also item in rhs.
 #
@@ -938,13 +937,44 @@ export def intersect (cmpFn: a => a => Order) (lhs: List a) (rhs: List a): List
 #   subset scmp ("", Nil) ("", "foo", "bar", Nil) = True
 #   subset scmp ("", "bat", Nil) ("", "foo", "bar", Nil) = False
 export def subset (cmpFn: a => a => Order) (lhs: List a) (rhs: List a): Boolean =
-    def lhsSort = sortBy cmpFn lhs
-    def rhsSort = sortBy cmpFn rhs
-
-    match lhsSort rhsSort
+    def subsetImp cmpFn lhsSort rhsSort = match lhsSort rhsSort
         Nil _ -> True
         _ Nil -> False
         (lh, lt) (rh, rt) -> match (cmpFn lh rh)
             LT -> False
-            GT -> subset cmpFn (lh, lt) rt
-            EQ -> subset cmpFn lt rt
+            GT -> subsetImp cmpFn (lh, lt) rt
+            EQ -> subsetImp cmpFn lt rt
+
+    subsetImp cmpFn (sortBy cmpFn lhs) (sortBy cmpFn rhs)
+
+# Returns a list of items where each item was a memeber of lhs but not rhs
+# The returned list will not be the same order as the parameters.
+#
+# Guarantees:
+#  - Output list length will be <= the length of lhs
+#  - All items in output list will be present in lhs
+#  - No items in output list will be present in rhs
+#  - Performance is considered and exceeds the naive N^2 algorithm
+#
+# Examples:
+# ```
+#   difference icmp (seq 4) (seq 3) = 3, Nil
+#   difference icmp (seq 3) (seq 3) = Nil
+#   difference icmp (seq 3) (2, Nil) = 0, 1, Nil
+#   difference scmp ("", "bar", "bat", Nil) ("", "foo", "bat", Nil) = "bar", Nil
+# ```
+export def difference (cmpFn: a => a => Order) (lhs: List a) (rhs: List a): List a =
+    def differenceImp cmpFn lhsSort rhsSort = match lhsSort rhsSort
+        # lhs is empty so the result will always be empty
+        Nil _ -> Nil
+        # rhs is empty nothing else to subtract so result will always be lhs
+        l Nil -> l
+        (lh, lt) (rh, rt) -> match (cmpFn lh rh)
+            # lh is smaller, add it to the output set then continue looking in lt
+            LT -> lh, (differenceImp cmpFn lt (rh, rt))
+            # rh is smaller so drop it, then continue looking in (lh, lt)
+            GT -> differenceImp cmpFn (lh, lt) rt
+            # item is in both sets. Remove it then continue looking
+            EQ -> differenceImp cmpFn lt rt
+
+    differenceImp cmpFn (sortBy cmpFn lhs) (sortBy cmpFn rhs)

tests/standard-library/list/pass.sh

@@ -16,3 +16,7 @@ WAKE="${1:+$1/wake}"
 "${WAKE:-wake}" --stdout=warning,report test12
 "${WAKE:-wake}" --stdout=warning,report test13
 "${WAKE:-wake}" --stdout=warning,report test14
+"${WAKE:-wake}" --stdout=warning,report test15
+"${WAKE:-wake}" --stdout=warning,report test16
+"${WAKE:-wake}" --stdout=warning,report test17
+"${WAKE:-wake}" --stdout=warning,report test18

tests/standard-library/list/stdout

@@ -12,3 +12,7 @@ True
 False
 True
 False
+3, Nil
+Nil
+0, 1, Nil
+"bar", Nil

tests/standard-library/list/test.wake

@@ -17,3 +17,9 @@ export def test11 _ = subset icmp Nil (seq 1)
 export def test12 _ = subset icmp (seq 1) Nil
 export def test13 _ = subset scmp ("", Nil) ("", "foo", "bar", Nil)
 export def test14 _ = subset scmp ("", "bat", Nil) ("", "foo", "bar", Nil)
+
+# difference tests
+export def test15 _ = difference icmp (seq 4) (seq 3)
+export def test16 _ = difference icmp (seq 3) (seq 3)
+export def test17 _ = difference icmp (seq 3) (2, Nil)
+export def test18 _ = difference scmp ("", "bar", "bat", Nil) ("", "foo", "bat", Nil)