[Oz] Generating lists of variables

[Raphael Collet]

> Hello,
> 
> I am currently working on a project related to the
> Frequency Allocation Problem, and its implementation
> through constraint programming. I have decided to use
> Oz for this project, but have yet to master it. I was
> therefore wondering if somebody could help me with the
> following difficulty:
> 
> One of the input used for this problem is the demand
> vector, which indicates the number of channel needed
> for each cell of the network. For example, the
> following input:
> 
> Demand = demand(5 7 3 5)
> 
> means that four cells exist in the network, and that
> their respective capacity are 5, 7, 3 and 5. Since
> each unit of capacity must be associated to a
> variable, the end results must therefore be a record
> like:
> 
> Channel = channel( (_ _ _ _ _) (_ _ _ _ _ _ _) (_ _ _)
> (_ _ _ _ _) )
> 
> where each "_" represents one of the needed variable.
> Unfortunatly, I have been unable to achieve such as
> result, even if it's somewhat basic. Does somebody
> have a helpfull suggestion on how to procede?

Yes.  I needed such things myself.  You can find very helpful basic
operations by browsing The Oz Base Environment documentation.  The
answer to your question is in section 6.2 Tuples.

{Tuple.make +L +I ?T} 

binds T to new tuple with label L and fresh variables at features 1
through I. I must be non-negative, else an error exception is raised. 
For example, {Tuple.make b 5} returns b(_ _ _ _ _).

Your problem can be solved by:

	Demand=demand(5 7 3 5)
	DemChan={Record.map Demand fun {$ I}
				      {Tuple.make c I}
				   end}
	Channel={Record.adjoin DemChan channel}

The record Demand is first mapped, and each element is applied a
function that creates a tuple with as many fields as its argument.
Second, all DemChan's fields are adjoined to channel, which is a record
with no field at all.  This is a trick for changing a record's label.
When finished, Channel is bound to

	channel(c(_ _ _ _ _) c(_ _ _ _ _ _ _) c(_ _ _) c(_ _ _ _ _))

Note that the inner tuples must have a label (all records have a label.)


Cheers.

--
Raphaël Collet
raph at info.ucl.ac.be
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