..
   This file is part of Logtalk <https://logtalk.org/>  
   Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.


.. index:: pair: logtalk_load/2; Built-in predicate
.. _predicates_logtalk_load_2:

logtalk_load/2
==============

Description
-----------

::

   logtalk_load(File, Flags)
   logtalk_load(Files, Flags)

Compiles to disk and then loads to memory a :term:`source file` or a list
of source files using a list of compiler flags. The Logtalk source file name
extension (by default, ``.lgt``) can be omitted. Source file paths can be
absolute, relative to the current directory, or use :term:`library notation`.
Compiler flags are represented as *flag(value)*. This predicate can also be
used to compile Prolog source files as Logtalk source code. When no recognized
Logtalk or Prolog extension is specified, the compiler tries first to append a
Logtalk source file extension and then a Prolog source file extension.
If that fails, the compiler tries to use the file name as-is. For a
description of the available compiler flags, please see the
:ref:`programming_flags` section in the User Manual.

When this predicate is called from the top-level, relative source file
paths are resolved using the current working directory. When the calls
are made from a source file, relative source file paths are resolved by
default using the source file directory (unless a
:ref:`relative_to <flag_relative_to>` flag is passed).

Note that only the errors related to problems in the predicate argument
are listed below. This predicate fails on the first error found during
compilation of a source file. In this case, no contents of the source
file are loaded.

.. warning::

   The compiler flags specified in the second argument only apply to the
   files listed in the first argument and not to any files that those files
   may load or compile. Notably, if you are loading a :term:`loader file`,
   the flags only apply to the loader file itself and not to the files
   loaded by it.

Modes and number of proofs
--------------------------

::

   logtalk_load(@source_file_name, @list(compiler_flag)) - zero_or_one
   logtalk_load(@list(source_file_name), @list(compiler_flag)) - zero_or_one

Errors
------

| File is a variable:
|     ``instantiation_error``
| Files is a variable or a list with an element which is a variable:
|     ``instantiation_error``
| File, or an element File of the Files list, is neither a variable nor a source file name:
|     ``type_error(source_file_name, File)``
| File, or an element File of the Files list, uses library notation but the library does not exist:
|     ``existence_error(library, Library)``
| File or an element File of the Files list, does not exist:
|     ``existence_error(file, File)``
| Flags is a variable or a list with an element which is a variable:
|     ``instantiation_error``
| Flags is neither a variable nor a proper list:
|     ``type_error(list, Flags)``
| An element Flag of the Flags list is not a valid compiler flag:
|     ``type_error(compiler_flag, Flag)``
| An element Flag of the Flags list defines a value for a read-only compiler flag:
|     ``permission_error(modify, flag, Flag)``
| An element Flag of the Flags list defines an invalid value for a flag:
|     ``domain_error(flag_value, Flag+Value)``

Examples
--------

::

   % compile and load the "list" source file in the
   % current directory using default compiler flags:
   | ?- logtalk_load(list, []).

   % compile and load the "tree" source file in the "types"
   % library directory with the source_data flag turned on:
   | ?- logtalk_load(types(tree)).

   % compile and load the "file_system" source file in the
   % current directory with portability warnings suppressed:
   | ?- logtalk_load(file_system, [portability(silent)]).

.. seealso::

   :ref:`predicates_logtalk_compile_1`,
   :ref:`predicates_logtalk_compile_2`,
   :ref:`predicates_logtalk_load_1`,
   :ref:`predicates_logtalk_make_0`,
   :ref:`predicates_logtalk_make_1`,
   :ref:`predicates_logtalk_library_path_2`
