2016 Update

Task/Stack/Standard-ML/stack-1.ml

@@ -0,0 +1,16 @@
+signature STACK =
+sig
+    type 'a stack
+    exception EmptyStack
+
+    val empty : 'a stack
+    val isEmpty : 'a stack -> bool
+
+    val push : ('a * 'a stack) -> 'a stack
+    val pop  : 'a stack -> 'a stack
+    val top  : 'a stack -> 'a
+    val popTop : 'a stack -> 'a stack * 'a
+
+    val map : ('a -> 'b) -> 'a stack -> 'b stack
+    val app : ('a -> unit) -> 'a stack -> unit
+end

Task/Stack/Standard-ML/stack-2.ml

@@ -0,0 +1,22 @@
+structure Stack :> STACK =
+struct
+    type 'a stack = 'a list
+    exception EmptyStack
+
+    val empty = []
+
+    fun isEmpty st = null st
+
+    fun push (x, st) = x::st
+
+    fun pop []      = raise EmptyStack
+      | pop (x::st) = st
+
+    fun top []      = raise EmptyStack
+      | top (x::st) = x
+
+    fun popTop st = (pop st, top st)
+
+    fun map f st = List.map f st
+    fun app f st = List.app f st
+end