Re: [isabelle] Making records instances of classes

Dear Philipp,

in Isabelle 2011, the type for extensible records is no longer called
<record name>_type_ext, but <record name>_ext. The NEWS file mentions this as follows:

> * Records: logical foundation type for records does not carry a
> '_type' suffix any longer (obsolete due to authentic syntax).

Hence, the following should work now:

record ('a, 'b) Tuple = first :: "'a" second :: "'b"
instance Tuple_ext :: (finite, finite, finite) finite

Hope this helps,

Philipp Küfner schrieb:
Dear all,

In July 2010 there was a discussion on Making records instances of
classes. As far as I can see the presented solution (see below) does not
work with the current version of Isabelle (2011) anymore (due to the new
implementation of records). So does anyone know how to handle this
problem now?

Thanks a lot,


On 09/07/2010, at 4:56 PM, Andreas Lochbihler wrote:
Behind the scenes, the package achieves this by defining a more general type for Tuple called Tuple_ext_type, which takes another type variable.
Then, the type ('a, 'b) Tuple is just a type abbreviation for ('a, 'b, unit) Tuple_ext_type. For subrecord types, this additional type variable is instantiated to some other type which stores the additional information.

Type classes can only be instantiated for "logical" type constructors, not for abbreviations like Tuple. In your example, you would have to instantiate Tuple_ext_type itself. Note that this instantiation then also applies to all subrecords you might ever define.

record ('a, 'b) Tuple = first :: "'a" second :: "'b"

instance Tuple_type_ext :: (finite, finite, finite) finite

Thanks Andreas!

Perhaps this could make its way into the distributed Isabelle documentation and/or examples?

Also Florian Haftmann sent me this complete chunk of proof text off-list, for which I am grateful:

record ('a, 'b) Tuple = first :: "'a" second :: "'b"

instance Tuple_ext_type :: (finite, finite, finite) finite
 let ?U = "UNIV :: ('a, 'b, 'c) Tuple_ext_type set"
 { fix x :: "('a, 'b, 'c) Tuple_scheme"
   have "∃a b c. x = Tuple_ext a b c"
     by (cases x) simp
 } then have U:
   "?U = (\<lambda>((a, b), c). Tuple_ext a b c) ` ((UNIV × UNIV) × UNIV)"
     by (auto simp add: image_def)
 show "finite ?U" by (simp add: U)


Karlsruher Institut für Technologie
IPD Snelting

Andreas Lochbihler
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KIT - Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der Helmholtz-Gemeinschaft

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