11.7 Guidelines

In this section we cover several guidelines on how to use CHR to write constraint solvers and how to do so efficiently.

• Set semantics: The CHR system allows the presence of identical constraints, i.e. multiple constraints with the same functor, arity and arguments. For most constraint solvers, this is not desirable: it affects efficiency and possibly termination. Hence appropriate simpagation rules should be added of the form:
  
  $$constraint \backslash constraint <=> true$$
  
  

• Multi-headed rules: Multi-headed rules are executed more efficiently when the constraints share one or more variables.