Dynamically loading predicates in the interpreter

Modules are usually loaded into an environment when they are consulted (see Section 3.7). Specific predicates from a module can also be imported into the run-time environment through the standard predicate import PredList from Module. Here, PredList can either be a Prolog list or a comma list. (The import/1 can also be used as a directive in a source module (see Section 3.3).

We provide a sample session for compiling, dynamically loading, and querying a user-defined module named quick_sort. For this example we assume that quick_sort is a file in the current working directory, and contains the definitions of the predicates concat/3 and qsort/2, both of which are exported.

             | ?- compile(quick_sort).
             [Compiling ./quick_sort]
             [quick_sort compiled, cpu time used: 1.439 seconds]

             yes
             | ?- import concat/3, qsort/2 from quick_sort. 

             yes
             | ?- concat([1,3], [2], L), qsort(L, S).

             L = [1,3,2]
             S = [1,2,3]

             yes.

The standard predicate import/1 does not load the module containing the imported predicates, but simply informs the system where it can find the definition of the predicate when (and if) the predicate is called.