On 07/09/2017 05:11 PM, Peter Brottveit Bock wrote:
Is it possible to generate a fresh name relative to some collection of names? I.e. something
of kind "gensym :: {Unit} -> Name".
Short answer: I can't think of any way to implement that feature, with
Ur as it stands today.
Does it break some nice meta-properties of Ur/Web?
It seems consistent with the model of Ur in Coq, though the
representation of rows might need to be extended to allow iteration even
without a folder (to find a fresh name).
I have two possible types which can be used to represent this:
val lolli_right :
t0 ::: Type -> t1 ::: Type -> gamma ::: {Type} ->
(n :: Name -> [[n] ~ gamma] => lin (gamma ++ [n = t0]) t1) ->
lin gamma (lolli t0 t1)
and
val lolli_right' :
n ::: Name -> t0 ::: Type -> t1 ::: Type -> gamma ::: {Type} ->
[[n] ~ gamma] =>
lin (gamma ++ [n = t0]) t1 ->
lin gamma (lolli t0 t1)
The first type is arguably nicer, since when used as a proof term, it actually binds the
name "n" locally. The second
version works, but it's not a binder proper, so it "pushes" the problem of
finding a suitable name further out. Said another way, the first version is modular while
the second is not.
While it is straight forward to implement the second version, I can not
immediately see a way to implement the first one, without a way to generate a
fresh name.
Well, you could combine the two: take in a polymorphic premise, but also
ask for a concrete disjoint name to be passed at the top level. The
implementation can instantiate the premise with the concrete name.
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