Appendix F  Restrictions and Limits

The ECLⁱPS^e implementation tries to impose as few limits as possible. The existing limits are:

1. The maximum arity of a predicate in ECLⁱPS^e is 255 (this value can be queried with get_flag(max_predicate_arity, X)). Note however that the arity of compound terms is unlimited.
2. The maximum arity of external predicates in the current implementation of ECLⁱPS^e is 16.
3. The stack and heap sizes have virtual memory limits which can be changed using the -g, -l, -s and -p command line options or the ec_set_option function in case of an embedded ECLⁱPS^e.
4. When the occur check is disabled (the default) it is possible (and sometimes useful) to create cyclic data structures. For example, the unification of X and g(X) in

   X = g(X)
   

   will result in a cyclic structure

       X = g(g(g(g(g(...)))))
   

   Not all ECLⁱPS^e built-in predicates handle cyclic terms gracefully. Care must be taken with all predicates which traverse the whole term, e.g., copy_term/2, term_hash/4, writeq/2, assert/1, compile_term/1. These will typically loop or overflow a stack when applied to cyclic terms. Note however that, starting from version 5.6, cyclic terms are allowed in all heap copying predicates (setval/2, bag_enter/2, shelf_set/3, store_set/3, record/2, etc.).