prolog_load_context/2

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Predicate prolog_load_context/2

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Availability:built-in

prolog_load_context(?Key, ?Value)

Obtain context information during compilation. This predicate can be used from directives appearing in a source file to get information about the file being loaded as well as by the term_expansion/2 and goal_expansion/2 hooks. See also source_location/2 and if/1. The following keys are defined:

Key	Description
`directory`	Directory in which `source` lives (absolute path)
`dialect`	Compatibility mode. See expects_dialect/1.
`file`	Similar to `source`, but returns the file being included when called while an include file is being processed (absolute path)
`module`	Module into which file is loaded
`reload`	`true` if the file is being reloaded. Not present on first load
`script`	Boolean that indicates whether the file is loaded as a script file (see -s)
`source`	File being loaded (absolute path). If the system is processing an included file, the value is the main file. Returns the original Prolog file when loading a `.qlf` file.
`stream`	Stream identifier (see current_input/1)
`term_position`	Start position of last term read. See also stream_property/2 (`position` property and stream_position_data/3.^{59Up to version 7.1.22, the position term carried fake data except for the line_count and had five arguments, where the position property of a stream only has four.}
`term`	Term being expanded by expand_term/2.
`variable_names`	A list of‘`Name` = `Var`’of the last term read. See read_term/2 for details.

The directory is commonly used to add rules to file_search_path/2, setting up a search path for finding files with absolute_file_name/3. For example:

:- dynamic user:file_search_path/2.
:- multifile user:file_search_path/2.

:- prolog_load_context(directory, Dir),
   asserta(user:file_search_path(my_program_home, Dir)).

    ...
    absolute_file_name(my_program_home('README.TXT'), ReadMe,
                       [ access(read) ]),
    ...