13.1.1 Loading Prolog files

The WASM build ships with the Prolog library and thus Prolog libraries can be loaded as normal using use_module/1, etc., for example, we can include the lists library using this directive. Note that the normal autoloading of library code works in the WASM version.

:- use_module(library(lists)).

When Prolog is in asynchronous mode, i.e., called through Prolog.forEach(), we can also load code from a URL. For example, we can load the CHAT80 demo program directly from GitHub using^{244The \c continues the quoted atom from the next line after removing leading white space.}

?- consult('https://raw.githubusercontent.com/JanWielemaker/\c
            chat80/master/prolog/chat80.pl').

Larger files can be loaded as .qlf files. See section 4.3.3 and qcompile/2. Notably we can create a single qlf file from an application using the include(user) option. Below we create a .qlf file from CHAT80. The resulting chat80.qlf can be loaded from a URL using consult/1 as above.

?- qcompile('chat80.pl', [include(user)]).

There are three ways to load Prolog code from JavaScript: (1) loading from a string, (2) loading from <script> elements and (3) loading from URL. Note that all the loading methods return a Promise that is resolved when loading the data is completed.

Promise Prolog.load_string(String, Id)

Load Prolog code from String, pretending it was loaded from the file Id. The Id is optional. When omitted it generates /string/1, /string/2, ... .

Promise Prolog.load_scripts()

Load all scripts from the current docement that have their type set to text/prolog. The file reference for the loaded script is /script/Id, where Id is derived from (1) the id of the script, (2) the name of the script or (3) being the nth Prolog script in the document. When resolved, the promise returns an array with the names of the loaded scripts.

Promise Prolog.consult(...Sources)

Load the given Sources. Each source is either a file from the local file system, e.g., library(lists) or a URL. The sources are downloaded and processed sequentially. This uses Prolog.forEach() calling load_files/1. The returned Promise returns 1 on success.