Random Bit of SML Code

[wtd]

Have fun figuring out how it works.

code:

signature BTREE_CONTENTS = sig    type t    val compare : t * t -> order end   functor BTree(X : BTREE_CONTENTS) = struct    type t = X.t      datatype btree =       Leaf     | Value of X.t     | Branch of X.t * btree * btree      fun contains(_, Leaf) = false      | contains(v, Value v') =          X.compare(v, v') = EQUAL      | contains(v, Branch (v', left, right)) =          (case X.compare(v, v') of             EQUAL   => true           | LESS    => contains(v, left)           | GREATER => contains(v, right));      fun insert(v, Leaf) = Value v      | insert(v, t as Value v') =          (case X.compare(v, v') of             EQUAL   => t           | LESS    => Branch (v', Value v, Leaf)           | GREATER => Branch (v', Leaf, Value v))      | insert(v, t as Branch (v', left, right)) =          (case X.compare(v, v') of             EQUAL   => t           | LESS    => Branch (v', insert(v, left), right)           | GREATER => Branch (v', left, insert(v, right)))      fun toList(Leaf) = []      | toList(Value v) = [v]      | toList(Branch (v, left, right)) =          toList(left) @ [v] @ toList(right)      fun height(Leaf) = 0      | height(Value _) = 1      | height(Branch (_, left, right)) =          Int.max(height(left), height(right)) + 1      fun size(Leaf) = 0      | size(Value _) = 1      | size(Branch (_, left, right)) =          1 + size(left) + size(right)      fun isBalanced(Leaf) = true      | isBalanced(Value _) = true      | isBalanced(Branch (_, left, right)) =          Int.abs(height(left) - height(right)) <= 1          andalso isBalanced(left)          andalso isBalanced(right) end   structure IntBTree = BTree(type t = int; val compare = Int.compare)