Compiler-Generated Predicates

Besides predicates for the defined constraints, the CHR compiler generates some support predicates in the module containing the handler. To avoid naming conflicts, the following predicates must not be defined or referred to by user code in the same module:

verify_attributes/3

attribute_goal/2

attach_increment/2

'attach_F/A'/2

for every defined constraint F/A.

'F/A_N_M_...'/Arity

for every defined constraint F/A. N and M is are integers, Arity > A.

For the prime number example that is:

             attach_increment/2
             attach_prime/1/2
             attach_primes/1/2
             attribute_goal/2
             goal_expansion/3
             prime/1
             prime/1_1/2
             prime/1_1_0/3
             prime/1_2/2
             primes/1
             primes/1_1/2
             verify_attributes/3
     

If an author of a handler wants to avoid naming conflicts with the code that uses the handler, it is easy to encapsulate the handler. The module declaration below puts the handler into module primes, which exports only selected predicates--the constraints in our example.

     :- module(primes, [primes/1,prime/1]).
     
     :- use_module(library(chr)).
     
     handler eratosthenes.
     constraints primes/1,prime/1.
     ...