I have a source file, openpage.pl, where I call use_module/1 to “import” SWI-Prolog’s http_open/3:
use_module(library(http/http_open)).
request(URL, In) :- http_open(URL, In, []),
copy_stream_data(In, user_output),
close(In).
It loads without complaint. However, try as I might, I can’t run it the rules in it.
?- [openpage].
% openpage compiled 0.00 sec, 1,828 bytes
true.
?- request('http://www.google.com', In).
ERROR: request/2: Undefined procedure: http_open/3
?- use_module(library(http/http_open)).
true.
?- request('http://www.google.com', In).
ERROR: request/2: Undefined procedure: http_open/3
?- make.
% Scanning references for 1 possibly undefined predicates
Warning: The predicates below are not defined. If these are defined
Warning: at runtime using assert/1, use :- dynamic Name/Arity.
Warning:
Warning: http_open/3, which is referenced by
Warning: status/2 at /home/dale/sesame_test/prolog/openpage.pl:16
Warning: request/2 at /home/dale/sesame_test/prolog/openpage.pl:3
Warning: modified/2 at /home/dale/sesame_test/prolog/openpage.pl:7
true.
?- [openpage].
% openpage compiled 0.00 sec, 616 bytes
true.
?- request('http://www.google.com', In).
ERROR: request/2: Undefined procedure: http_open/3
?-
[forced] Action (h for help) ? exit
So in my next session, I invoke use_module/1 before loading my source file, and all is fine:
?- use_module(library(http/http_open)).
% library(uri) compiled into uri 0.00 sec, 199,772 bytes
% library(readutil) compiled into read_util 0.00 sec, 10,312 bytes
% library(socket) compiled into socket 0.00 sec, 6,376 bytes
% library(option) compiled into swi_option 0.00 sec, 7,748 bytes
% library(base64) compiled into base64 0.00 sec, 9,776 bytes
% library(debug) compiled into prolog_debug 0.01 sec, 12,056 bytes
% library(http/http_open) compiled into http_open 0.01 sec, 282,844 bytes
true.
?- [openpage].
% openpage compiled 0.00 sec, 1,380 bytes
true.
?- request('http://www.google.com/', In).
<!doctype html><html itemscope itemtype="http://schema.org/WebPage">
...
In = <stream>(0x9366508).
How can I set up and execute my files so that I don’t need this manual step of loading modules before loading my own code?
Try:
in your source file.