[racket] Datalog: summing

In typical Prolog the simplest way would be to use aggregate:

http://www.swi-prolog.org/pldoc/doc_for?object=section(2,'A.1',swi('/doc/Manual/aggregate.html'))

<http://www.swi-prolog.org/pldoc/doc_for?object=section(2,'A.1',swi('/doc/Manual/aggregate.html'))>

In Racklog you can simply use bag-of to generate a list of your facts
satisfying some predicate, then sum it on the Racket side eg. using foldl.

Similar for Datalog - you can generate list by Datalog querying, then sum
via regular Racket functions.



On Mon, Sep 19, 2011 at 11:25, Mark Carter <mcturra2000 at yahoo.co.uk> wrote:

> How do I create summing rules?
>
> Suppose I have the following facts:
>
> post(cash, 26) .
> post(cash, -16) .
> post(cash, 50) .
> post(beer, 20) .
>
>
> How do I create a rule "bal"
> bal(X, ???)
> such that the ??? gives me the sum of the second arguments in post
> satisfying the first argument X?
>
> Also, is there a way of writing floats, or is that out of the question?
>
>
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