The Load Predicates

Loading a program is accomplished by one of these predicates

load_files(File)

compiles source file or loads QOF file, whichever is the more recent. load_files(File) can also be written as [File].

compile(File)

compiles source file.

consult(File)

Same as compile

ensure_loaded(File)

loads more recent of source and QOF files, unless the file has already been loaded and it has not been modified since it was loaded.

load_files(File, Options)

loads file according to the specified options. All the above predicates can be regarded as special cases of this one.

reconsult(Files)

same as consult

The following notes apply to all the Load Predicates:

1. The File argument must be one of:
   • an atom that is the name of a file containing Prolog code; a .pl or a .qof suffix to a filename may be omitted (see ref-fdi-fsp-fde;)
   • a list of any atom listed above;
   • the atom user

   Please note: If the filename is not a valid atom, it must be enclosed in single quotes. For example,

                  load_files(expert)
                  load_files('Expert')
                  compile('/usr/joe/expert')
                  ensure_loaded('expert.pl')
                  

2. These predicates resolve relative file names in the same way as absolute_file_name/2. For information on file names refer to ref-fdi.
3. The above predicates raise an exception if any of the files named in File does not exist, unless the fileerrors flag is set to off using nofileerrors/0.

   Errors detected during compilation, such as an attempt to redefine a built-in predicate, also cause exceptions to be raised. However, these exceptions are caught by the compiler, and an appropriate error message is printed.

4. There are a number of style warnings that may appear when a file is compiled. These are designed to aid in catching simple errors in your programs, but some or all of them can be turned off if desired using no_style_check/1. The possible style warnings are:
   1. A named variable occurs only once in a clause. Variables beginning with a _ are considered not named.
   2. All the clauses for a predicate are not adjacent to one another in the file.
   3. A predicate is being redefined in a file different from the one in which it was previously defined.
5. By default, all clauses for a predicate are required to come from just one file. A predicate must be declared multifile if its clauses are to be spread across several different files. See the reference page for multifile/1.
6. If a file being loaded is not a module-file, all the predicates defined in the file are loaded into the source module. The form load_files(Module:File) can be used to load the file into the specified module. See ref-mod-def, for information about module-files. If a file being loaded is a module-file, it is first loaded in the normal way, then the source module imports all the public predicates of the module-file except for use_module and load_file if you specify an import list.
7. If there are any directives in the file being loaded, that is, any terms with principal functor :-/1 or ?-/1, then these are executed as they are encountered. A common type of directive to have in a file is one that loads another file, such as

              :- [otherfile].
             

   In this case, if otherfile is a relative filename it is resolved with respect to the directory containing the file that is being loaded, not the current working directory of the Prolog system.

   Any legal Prolog goal may be included as a directive. Note, however, that if the file is compiled by qpc, the goal will be executed by qpc, not when the .qof file is loaded or when application begins execution. The initialization/1 declaration provides this functionality. There is no difference between a :-/1 and a ?-/1 goal in a file being compiled.

8. If File is the atom user, or File is a list, and during loading of the list user is encountered, procedures are to be typed directly into Prolog from the terminal. A special prompt, | , is displayed at the beginning of every new clause entered from the terminal. Continuation lines of clauses typed at the terminal are preceded by a prompt of five spaces. When all clauses have been typed in, the last should be followed by an end-of-file character.
9. Terms that are notational variants of Prolog terms, notably grammar terms, are expanded into Prolog code during compilation. By defining the hook predicate term_expansion/2 (in module user), you can specify any desired transformation to be done as clauses are loaded.
10. Any predicates that need to be called during the compilation of a file, including term_expansion/2 and all the predicates it calls, must be treated specially if you wish to be able to compile that file with qpc. See sap-srs-eci-crt for information on this.
11. The current load context (module, file, stream, directory) can be queried using prolog_load_context/2.