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eduardoleon/mtc-elab.sml

Created July 11, 2016 16:11
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Modular type classes are defined by elaboration
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mtc-elab.sml
using IntOrd
(* `Heap` elaborates to `Heap(IntOrd)`,
* so `val xs : Heap(IntOrd).t` *)
val xs = Heap.fromList [1,2,3];
(* shadows previous `using` declaration *)
using Backwards(IntOrd)
(* `Heap` elaborates to `Heap(Backwards(IntOrd))`,
* so `val ys : Heap(Backwards(IntOrd)).t` *)
val ys = Heap.fromList [1,2,3];
(* type error: can't unify `xs`'s type `Heap(IntOrd).t`
* with expected type `Heap(Backwards(IntOrd)).t` *)
val zs = Heap.merge (xs, ys)
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