Preserve / Output CLP Ranges for Query

[rindPHI]

Hi all,

I'm currently working with queries that output "abstract" terms containing CLP variables with bounded domain. For instance, a direct swipl query returns:

S = [stmt, [[assgn, [[var, [[_15304, []]]], [" := ", []], [rhs, [[digit, [[_15382, []]]]]]]]]],
_15304 in 120..122,
_15382 in 49..51

I did not find any way to retrieve the bounds 120..122 etc. for the contained variables; I only get the instantiation of S. Unfortunately, I need this information for further processing. Do you have any idea for solutions to that problem?

Thanks in advance and Best Regards, Dominic

[rindPHI]

OK, I thought I found a solution by applying a trick suggested by the clpfd documentation: Making the constraints involved in a term explicit by calling copy_term:

stmt(S), term_variables(S, Vs), copy_term(Vs, Vs, Gs).

However, the variables Gs have different handles than those in S, which they don't when I run this directly in the swipl interface. The names of these variables are something like _123, so they don't have the chars property set. Is there any way to fix this issue (i.e., same handles for same variables, or some workaround to check whether two variables w/ different handle actually represent the same variables)?

Thanks again!

/edit:

From swipl, I get the output

?- stmt(X), term_variables(X, Vs), copy_term(Vs, Vs, Gs).
X = [stmt, [[assgn, [[var, [[_34850, []]]], [" := ", []], [rhs, [[digit, [[_34928, []]]]]]]]]],
Vs = [_34850, _34928],
Gs = [clpfd:(_34850 in 120..122), clpfd:(_34928 in 49..51)],
_34850 in 0..10,
_34928 in 0..9 

whereas pyswip gives my

(["'stmt'", [["'assgn'", [["'var'", [['_155', []]]], ['" := "', []], ["'rhs'", [["'digit'", [['_181', []]]]]]]]]], 
['_208 in 0..10', '_215 in 0..9'])

Please ignore the different quotation marks; that's since these are Python strings. I translated the expressions from the pyswip objects to strings with a method I wrote myself, the _208 etc. are obtained by calling variable.handle. Note the different handles, which refer to different variables after translation to string.

If it necessary to know, the original string representation of the pyswip query result is

{'S': [Atom('919813'), [[Atom('919941'), [[Atom('110981'), [[Variable(174), []]]], [b' := ', []], [Atom('920325'), [[Atom('110981'), [[Variable(200), []]]]]]]]]], 
'Vs': [Variable(217), Variable(218)],
'Gs': [Functor(192781,2,clpfd,in(Variable(227), ..(0, 10))), Functor(192781,2,clpfd,in(Variable(234), ..(0, 10)))]}

All variable handles are different...

[rindPHI]

OK, kind of got it... Variables w/ different handles can represent the same prolog variable, which you find out by comparing them with standard Python equality ==. So when I translate those to a Prolog string, I have to "unify" (not in the Prolog sense!) the variable names for equal variables. Another trap was that I wanted to do this inside a list comprehension, and there equality checks did not work. Obviously the corresponding information about the handles got lost in between. Now I'm using a loop, and it works.

Is there any better procedure to convert a query result s.t. equal variables have the same handle? This would be quite useful and less confusing for beginners, I guess...