built-in predicate



logtalk_load_context(Key, Value)

Provides access to the Logtalk compilation/loading context. The following keys are currently supported:

  • entity_identifier - identifier of the entity being compiled if any
  • entity_prefix - internal prefix for the entity compiled code
  • entity_type - returns the value module when compiling a module as an object
  • source - full path of the source file being compiled
  • file - the actual file being compiled, different from source only when processing an include/1 directive
  • basename - source file basename
  • directory - source file directory
  • stream - input stream being used to read source file terms
  • target - the full path of the intermediate Prolog file
  • flags - the list of the explicit flags used for the compilation of the source file
  • term - the source file term being compiled
  • term_position - the position of the term being compiled (StartLine-EndLine)
  • variables - the variables of the term being compiled ([Variable1, ...])
  • variable_names - the variable names of the term being compiled ([Name1=Variable1, ...])
  • singletons - the singleton variables of the term being compiled ([Name1=Variable1, ...])

This predicate is usually called by the term_expansion/2 and goal_expansion/2 methods. It can also be called directly from initialization/1 directives in a source file. Note that the entity keys are only available when compiling an entity term or from an object initialization/1 directive.


The term_position key is only supported in backend Prolog compilers that provide access to the start and end lines of a read term. When such support is not available, the value -1 is returned for both the start and the end lines.

Currently, any variables in the values of the term, variables, variable_names, and singletons keys are not shared with, respectively, the term and goal arguments of the term_expansion/2 and goal_expansion/2 methods.

Using the variables, variable_names, and singletons keys may require calling the standard built-in predicate term_variables/2 on the term read and unifying the term variables with the variables in the names list. This, however, may rise portability issues with Prolog compilers that don’t return the variables in the same order for the term_variables/2 predicate and the option variable_names/1 of the read_term/3 built-in predicate, which is used by the Logtalk compiler to read source files.

Modes and number of proofs

logtalk_load_context(?atom, -nonvar) - zero_or_more




% expand source file terms only if they are entity terms
term_expansion(Term, ExpandedTerms) :-
    logtalk_load_context(entity_identifier, _),

% define a library alias based on the source directory
:- initialization((
    logtalk_load_context(directory, Directory),
    assertz(logtalk_library_path(my_app, Directory))