More on functions

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+//// A module containing some unusual functions and types.
+
+/// A type where the value can never be constructed.
+/// Can you work out why?
+pub type Never {
+  Never(Never)
+}
+
+/// Call a function twice with an initial value.
+///
+pub fn twice(argument: value, function: fn(value) -> value) -> value {
+  function(function(argument))
+}
+
+/// Call a function three times with an initial value.
+///
+pub fn thrice(argument: value, function: fn(value) -> value) -> value {
+  function(function(function(argument)))
+}