7.6 Backwards Compatibility

7.6.1 The Old SICStus CHR implemenation

There are small differences between the current K.U.Leuven CHR system in SWI-Prolog, older versions of the same system and SICStus' CHR system.

The current system maps old syntactic elements onto new ones and ignores a number of no longer required elements. However, for each a deprecated warning is issued. You are strongly urged to replace or remove deprecated features.

Besides differences in available options and pragmas, the following differences should be noted:

7.6.2 The Old ECLiPSe CHR implemenation

The old ECLiPSe CHR implementations 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 .