Artyom Shalkhakov wrote:
Hello,
Looking through basis.urs in the latest stable version, one finds:
con serialized :: Type -> Type
val serialize : t ::: Type -> t -> serialized t
val deserialize : t ::: Type -> serialized t -> t
val sql_serialized : t ::: Type -> sql_injectable_prim (serialized t)
The question are
- what are type families
- how to use sql_serialized
Having played a bit with type families of Haskell, I tend to think
that they are type-level functions, defined by induction on the
structure of input types. That is, a type family is defined by
clauses, where each clause can employ some sort of pattern matching
over it's input types. Is this intuition correct? What are type
families in Ur?
Ur includes a copy of System F (the polymorphic lambda calculus) at the
type level. Type families are just type-level functions, with none of
the incidental restrictions that are attached in Haskell. It turns out
you don't need to worry at all about these details to use [serialized],
though.
Serialization is supported specially by the compiler, so it's about as
easy to use as it could be. You don't need to do it any differently for
any types. Rather, you'll get a compile-time error if you try to
serialize a type that contains a function arrow or one of a few other
unsupported constructs. Beyond that, you can do the following for any
type, with no additional code required:
type t = ...
val x : t = ...
val ser : serialized t = serialize x
val x' : t = deserialize ser
(The example isn't meant to suggest that you need to do
[de]serialization in top-level declarations.)
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