Re: [isabelle] efficient code for ('a, 'b) map (as opposed to ('a, 'b) mapping



Ah, right. I somehow repressed that "'a set" is no longer a type synonym, which was the only reason why I was wondering about "('a, 'b) map". Now everything is clear (including that my question was stupid ;)).

cheers

chris

On 10/24/2013 06:35 PM, Peter Lammich wrote:
Hi Christian.

The problem is, that ('a,'b) map is just syntactic sugar for the type
'a => 'b option. The code-generator replacement of types by efficient
implementations only works for types represented by a single
type-constant (like ('a,'b) mapping or 'a set).

Moreover, note that, in general, you do not want to translate all
occurences of "'a -> 'b option" by a map implementation, as there are
also functions that return option-values, which are intended to be
translated as functions.


The automatic refinement framework [1] tries to tackle this problem,
however, it has to be employed manually before code generation, and
usually requires some setup overhead.

In order to use Containers, I believe that you should transform your
functions to use mapping. Maybe the transfer+lifting package of Brian
and Ondra may help you to automate this task.


Best,
   Peter

[1]: Peter Lammich, Automatic Data Refinement, Proc. of ITP 2013


On Do, 2013-10-24 at 18:10 +0900, Christian Sternagel wrote:
Dear all (especially Andreas ;)),

is it possible to automatically get efficient code when code generating
a function involving the "('a, 'b) map" type (i.e., "'a => 'b option").

If I import AFP/Containers I can have this for "('a, 'b) mapping" (which
is a type-copy of "('a, 'b) map").

But in the actual formalization "('a, 'b) map" is more convenient to use
since we have nice syntax like "m x" for lookup and "m (x |-> t)" for
update.

Since according to the user guide the above is possible w.r.t. "'a set",
I was wondering what the obstacle is for "('a, 'b) map" (or maybe I just
misunderstood something).

More concretely, what is your advice for a function like

    match_list ::
      (('f, 'v) term * ('f, 'v) term) list =>
        ('v => ('f, 'v) term option) => ('f, 'v) subst

where "match_list E Map.empty" gives a matcher for all equations in "E".
Would you change this to use "('v, ('f, 'v) term) mapping" instead, or
is there a way to get efficient code as it is? Thanks in advance!

cheers

chris








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