all done

sml/week1/date.sml

@@ -54,6 +54,22 @@ fun range from to =
         generate from to [] |> reverse
     end
 
+fun empty lst = lst = []
+
+(* not efficient but works *)
+fun exists elem lst =
+    filter (fn needle => elem = needle) lst |> empty |> not 
+
+fun uniqe lst =
+    let
+        fun find_uniqe elem uniqe_elems =
+            if (exists elem uniqe_elems)
+            then uniqe_elems
+            else elem :: uniqe_elems
+    in
+        fold find_uniqe [] lst
+    end
+
 (* naive sort, will blow up the stack. Can't use pattern matching for now :( *)
 (* fun sort f lst =
     case lst of
@@ -200,4 +216,16 @@ fun oldest (dates: Date list): Date option =
         if dates = []
         then NONE
         else sort compare dates |> hd |> SOME   
-    end
+    end
+
+fun number_in_months_challenge (
+    dates: Date list, 
+    months_to_find: int list
+): int =
+    number_in_months (dates, uniqe months_to_find)
+
+fun dates_in_months_challenge (
+    dates: Date list, 
+    in_months: int list
+): Date list =
+    dates_in_months (dates, uniqe in_months)

sml/week1/date_tests.sml

@@ -1,12 +1,15 @@
 use "test.sml";
 use "date.sml";
 
-
 val () =
     assert
         (range 1 2 = [1, 2])
         "range: generates sequence in right order" 
 
+val () = assert
+        (exists 1 [] = false)
+        "exists: empty list" 
+
 val () = assert (sort (fn a => fn b => a > b)  [] = []) "sort: empty list"
 val () = assert (sort (fn a => fn b => a > b)  [1] = [1]) "sort: one val"
 val () = 
@@ -236,7 +239,7 @@ val () =
         val dates = []
         val expect = NONE 
     in
-        assert (oldest dates = expect) "oldest: retruns NONE on empty list"
+        assert (oldest dates = expect) "oldest: returns NONE on empty list"
     end
 
 val () =
@@ -244,7 +247,7 @@ val () =
         val dates = [(2000, 11, 31)]
         val expect = SOME (2000, 11, 31)
     in
-        assert (oldest dates = expect) "oldest: retruns SOME date"
+        assert (oldest dates = expect) "oldest: returns SOME date"
     end
 
 val () =
@@ -252,7 +255,29 @@ val () =
         val dates = [(2020, 11, 31), (2021, 11, 31)]
         val expect = SOME (2020, 11, 31)
     in
-        assert (oldest dates = expect) "oldest: retruns oldest"
+        assert (oldest dates = expect) "oldest: returns oldest"
+    end
+
+val () =
+    let
+        val dates = [(2000, 11, 31), (2000, 11, 31)]
+        val months = [11, 11]
+        val expect = 2
+    in
+        assert
+            (number_in_months_challenge (dates, months) = expect)
+            "number_in_months_challenge: ignore month duplicates"
+    end
+
+val () =
+    let
+        val dates = [(2000, 11, 31), (2000, 12, 30),  (2000, 12, 31)]
+        val months = [11, 11]
+        val expect = [(2000, 11, 31)]
+    in
+        assert
+            (dates_in_months_challenge (dates, months) = expect)
+            "dates_in_months_challenge: ignore month duplicates"
     end
 
 val () = complete ()

sml/week1/operators.sml

@@ -10,8 +10,12 @@
 *)
 fun |> (x, f) = f x
 
-(* composition operator *)
+(* apply operator *)
 fun $ (f, x) = f x
 
+(* composition operator *)
+fun >> (f, g) x = g(f(x))
+
 infix |>
-infix $
+infix $
+infix >>