[Oz] Generating lists of variables

[Raphael Collet]

> Thank you both for your assistance, it has been very
> helpfull. If I could now beg your indulgence for a
> further a question:
> 
> I have now succesfully created the record "channel"
> and implemented a series of constraints. However, the
> distribution still eludes me. At first I tried to
> distribute directly on the record:
> 
>    {FD.distribute ff Channel}
> 
> but it gave me the following error message:
> 
> %*************************** type error
> *************************
> %**
> %** Expected type: vector of finite domains
> %** At argument:   1
> %** In statement:  {FDP.distribute 1 0
> channel(c(_{1#27} _{4#27} _{7#27} _{10#27} _{13#30})
> c(_{1#27} _{4#27} _{7#27} _{10#27} _{13#27} _{16#27}
> _{19#30}) c(_{1#27} _{4#27} _{7#30}) c(_{1#27} _{4#27}
> _{7#27} _{10#27} _{13#30})) _}
> %**
> %** Call Stack:
> %** procedure 'FdDistribute' in file
> "/home/mozart/httpd/html/build/build-1.1.0/mozart/share/lib/cp/FD.oz",
> line 506, column 6, PC = 5198140
> %**--------------------------------------------------------------

FD.distribute expects as argument a vector of finite domains, e.g., a
list of FD variables or a record of FD variables.  Channel is a record
of records of FD variables!

> So I instead tried to distribute on "Root", defined
> as:
>    Root = {List.flatten Channel}
> 
> but it still gave the same result. I then added the
> use of the Record.toList, but it still didn't change
> anything. I can distribute just fine on the individual
> sub-record of Channel, but never on the whole thing.
> What am I doing wrong?

First, Channel is NOT a list, so {List.flatten Channel} returns Channel
as result.  Second, {Record.toList Channel} gives you a list of records
of FD variables.  You just cannot distribute on such a thing, for the
reason I explained above.

Now we are close to a solution.  FD.distribute is used to specify the
order variables will be chosen and the strategy for distribution.
Actually, the following two lines are equivalent:

	{FD.distribute ff [X Y]}
	{FD.distribute ff [X]} {FD.distribute ff [Y]}

Thus, you can specify the distribution strategy you expect by saying:
"Distribute on the first subrecord, then distribute on the second
subrecord, etc."  This is done by distributing on each field of Channel:

	{Record.forAll Channel proc {$ X}
				  {FD.distribute ff X}
			       end}

I hope this sheds light on the matter.

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