Module expressions

[PaulBone]

In a dynamic language like Python you can selectively import different modules depending on configuration. We could achieve something a little like that by importing both modules but choosing which symbols to use at runtime with indirect calls. Consider.

func makeTree(xs : List('x)) -> Tree('x) {
   var T
   if length(xs) < 100 {
      T = import BTree
   } else {
      T = import RBTree
   }
   var $tree = T.new()
   for (x : xs) {
      T.insert(x, $tree)
   }
   return $tree
}

This example assumes some other syntaxes we don't have yet, and the return value isn't well typed. It's more like pseudo code.

At runtime T doesn't actually point to the module, instead T.new and T.insert point to the only two symbols required and the calls are indirect. They may be tupled but to tuple or not-tuple is an optimisation. Both modules need to be present during compilation this is not the same thing as dynamic linking.