adam@6: (** Derived functions dealing with polymorphic variants *)
adam@6: 
adam@6: val read : r ::: {Unit} -> t ::: Type -> folder r -> $(mapU t r) -> variant (mapU {} r) -> t
adam@6: val write : r ::: {Unit} -> t ::: Type -> folder r -> $(mapU t r) -> variant (mapU {} r) -> t -> $(mapU t r)
adam@6: 
adam@6: val search : r ::: {Unit} -> t ::: Type -> (variant (mapU {} r) -> option t) -> folder r -> option t
adam@6: val find : r ::: {Unit} -> (variant (mapU {} r) -> bool) -> folder r -> option (variant (mapU {} r))
adam@6: 
adam@6: val test : nm :: Name -> t ::: Type -> ts ::: {Type} -> [[nm] ~ ts] => folder ([nm = t] ++ ts)
adam@6:                                                                     -> variant ([nm = t] ++ ts) -> option t
adam@6: val testLess : nm :: Name -> t ::: Type -> ts ::: {Type} -> [[nm] ~ ts] => folder ts -> variant ([nm = t] ++ ts) -> option t
adam@6: 
adam@21: val weaken : r1 ::: {Type} -> r2 ::: {Type} -> [r1 ~ r2] => folder r1
adam@21:              -> variant r1 -> variant (r1 ++ r2)
adam@21: 
adam@6: val testEq : K --> f :: (K -> Type) -> nm :: Name -> t ::: K -> ts ::: {K} -> r ::: {K} -> [[nm] ~ ts] =>
adam@6:     Eq.eq r ([nm = t] ++ ts)
adam@6:     -> folder r
adam@6:     -> variant (map f r) -> option (f t)
adam@6: 
adam@6: val eq : r ::: {Unit} -> folder r -> variant (mapU {} r) -> variant (mapU {} r) -> bool
adam@6: 
adam@6: val makeEq : K --> f :: (K -> Type) -> nm :: Name -> t ::: K -> ts ::: {K} -> r ::: {K} -> [[nm] ~ ts] =>
adam@6:     Eq.eq r ([nm = t] ++ ts)
adam@6:     -> f t
adam@6:     -> variant (map f r)
adam@6: 
adam@21: val mp : r ::: {Unit} -> t ::: Type -> folder r -> (variant (mapU {} r) -> t) -> $(mapU t r)
adam@21: 
adam@6: val fold : r ::: {Unit} -> t ::: Type -> folder r -> (variant (mapU {} r) -> t -> t) -> t -> t
adam@6: 
adam@20: val foldR : tr ::: Type -> r ::: {Unit} -> t ::: Type -> folder r -> (variant (mapU {} r) -> tr -> t -> t) -> $(mapU tr r) -> t -> t
adam@20: 
adam@20: val appR : m ::: (Type -> Type) -> monad m
adam@20:            -> tr ::: Type -> r ::: {Unit} -> folder r -> (variant (mapU {} r) -> tr -> m {}) -> $(mapU tr r) -> m {}
adam@20: 
adam@21: val mapR : tr ::: Type -> t ::: Type -> r ::: {Unit} -> folder r -> (variant (mapU {} r) -> tr -> t) -> $(mapU tr r) -> $(mapU t r)
adam@21: 
adam@6: val destrR : K --> f :: (K -> Type) -> fr :: (K -> Type) -> t ::: Type
adam@6:              -> (p :: K -> f p -> fr p -> t)
adam@6:              -> r ::: {K} -> folder r -> variant (map f r) -> $(map fr r) -> t
adam@6: 
adam@6: val destr2R : K --> f1 :: (K -> Type) -> f2 :: (K -> Type) -> fr :: (K -> Type) -> t ::: Type
adam@6:              -> (p :: K -> f1 p -> f2 p -> fr p -> t)
adam@6:              -> r ::: {K} -> folder r -> variant (map f1 r) -> variant (map f2 r) -> $(map fr r) -> option t
ezyang@27: 
ezyang@27: (* Metaprogrammed type-directed case-match.
ezyang@27: 
ezyang@27: This uses a combination of type classes and metaprogramming to make
ezyang@27: it easy to write case-matches on very large variants with many
ezyang@27: similar elements.  Here's how you use it:
ezyang@27: 
ezyang@27:     1. For every type in the variant, write a local typeclass function
ezyang@27:        which reduces it to t, and register as such using the 'declareCase'
ezyang@27:        function in the module you created.
ezyang@27: 
ezyang@27:             let val empty = declareCase (fn _ (_ : int) => True)
ezyang@27: 
ezyang@27:        These functions also take an initial argument, which has
ezyang@27:        type [a -> variant ts]; e.g. you can use this to create
ezyang@27:        a new copy of the variant with different values!
ezyang@27:        Make sure you specify type signatures on the argument [t]
ezyang@27:        so that we can identify who this typeclass is for.  (If you
ezyang@27:        use type classes to construct the return value, you may
ezyang@27:        also need to declare the return type explicitly.)
ezyang@27: 
ezyang@27:     2. Do the match using 'typeCase':
ezyang@27: 
ezyang@27:             typeCase t
ezyang@27: 
ezyang@27:        If you need to override specific constructors, use this idiom:
ezyang@27: 
ezyang@27:             @typeCase t (_ ++ {
ezyang@27:                 YourConstr = declareCase (fn _ _ => ...)
ezyang@27:             }) _
ezyang@27: 
ezyang@27: How does it work?  Very simple: it uses local typeclasses + Ur/Web's
ezyang@27: support for automatically instantiating records of typeclasses.
ezyang@27: *)
ezyang@27: 
ezyang@27: class type_case :: {Type} -> Type -> Type -> Type
ezyang@27: val declareCase : ts ::: {Type} -> t ::: Type -> a ::: Type -> ((a -> variant ts) -> a -> t) -> type_case ts t a
ezyang@27: val typeCase : ts ::: {Type} -> t ::: Type -> variant ts -> $(map (type_case ts t) ts) -> folder ts -> t