8.6.2 The Old ECLiPSe CHR implemenation

The old ECLiPSe CHR implementation features a label_with/1 construct for labeling variables in CHR constraints. This feature has long since been abandoned. However, a simple transformation is all that is required to port the functionality.

label_with Constraint1 if Condition1.
...
label_with ConstraintN if ConditionN.
Constraint1 :- Body1.
...
ConstraintN :- BodyN.

is transformed into

:- chr_constraint my_labeling/0.

my_labeling \ Constraint1 <=> Condition1 | Body1.
...
my_labeling \ ConstraintN <=> ConditionN | BodyN.
my_labeling <=> true.

Be sure to put this code after all other rules in your program! With my_labeling/0 (or another predicate name of your choosing) the labeling is initiated, rather than ECLiPSe's chr_labeling/0 .