From: "François Pottier" <francois.pottier@inria.fr>
To: Andreas Rossberg <rossberg@mpi-sws.org>,
Peter Thiemann <thiemann@informatik.uni-freiburg.de>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] coinductive data types
Date: Wed, 31 Aug 2022 15:49:38 +0200 [thread overview]
Message-ID: <a1c5433b-afb8-d77c-b592-fa4027b6889d@inria.fr> (raw)
In-Reply-To: <9C63A771-E4AD-42E4-A889-56CB1FFB563E@mpi-sws.org>
Le 31/08/2022 à 11:41, Andreas Rossberg a écrit :
> yes, I think they are different things. With (nominal) algebraic data types:
>
> type peano = Z | S of peano
> type nat = Z | S of nat
> let f (x : peano) : nat = x -- type error
>
> But with iso-recursive types:
>
> type peano = mu peano. 1 + peano
> type nat = mu nat. 1 + nat
> let f (x : peano) : nat = x -- ok
Good point! Indeed, in the second example, peano and nat are plain
abbreviations for the same type (which happens to be a recursive
type), up to alpha-equivalence. So, not even an explicit coercion
is needed to convert x from peano to nat.
--
François Pottier
francois.pottier@inria.fr
http://cambium.inria.fr/~fpottier/
next prev parent reply other threads:[~2022-08-31 13:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-29 15:43 Aaron Gray
2022-08-30 7:24 ` François Pottier
2022-08-30 11:11 ` Xavier Leroy
2022-08-30 12:33 ` Aaron Gray
2022-08-31 1:21 ` Jacques Garrigue
[not found] ` <11E3A59A-BD33-4EC0-9FAD-711A1EACA35E@gmail.com>
2022-08-31 3:22 ` Aaron Gray
2022-09-01 12:13 ` Jacques Garrigue
2022-08-30 12:37 ` Aaron Gray
2022-08-30 13:57 ` Nate Foster
2022-08-30 15:27 ` Aaron Gray
2022-08-30 15:47 ` François Pottier
2022-08-30 16:32 ` Aaron Gray
2022-08-31 8:19 ` François Pottier
2022-08-30 16:45 ` Andreas Rossberg
2022-08-30 17:01 ` Aaron Gray
2022-08-30 18:20 ` Nate Foster
2022-08-31 8:25 ` François Pottier
2022-08-31 8:46 ` Peter Thiemann
2022-08-31 9:41 ` Andreas Rossberg
2022-08-31 13:49 ` François Pottier [this message]
2022-08-31 15:40 ` Peter Thiemann
2022-08-31 16:44 ` Andreas Rossberg
2022-08-31 15:55 ` Basile Clement
2022-08-31 18:42 ` Andreas Rossberg
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