How can I see the stdout for processes in sweeprolog?

General
1

Say I’m working on a server, that I start with a call like http_server(http_dispatch, [port(Port)])., right in the sweep top-level.

And in the server code I sometimes use format/1, but I don’t see any output in the top-level nor in any buffers in emacs. Compare this to running the server from a swipl top level, where I get to see the output. How can I see what is been printed?

@oskardrums

2

Of course, just after I posted this question, I found the async query functionality at
Sweep: SWI-Prolog Embedded in Emacs, but interestingly the output I get is:

starting server on port 8081
Sweep async goal finished

Process ?- server:start. finished

The code for server:start was:

start :-
    Port = 8081,
    format('starting server on port ~w', [Port]),
    http_server(http_dispatch, [port(Port)]).

In the meanwhile, the server still runs, and the result is not showed in the async goal buffer.

3

It seems that the premise of the question was wrong. The problem is that I should have used:

    format(user_output,"Node was: ~k~n",[Node]).

instead of

    format("Node was: ~k~n",[Node]).

as I had done before, but forgot. If I do this, everything works as I expected. I’ll leave the question here nonetheless because it could be useful to someone else that encouters the same pitfall.

1 Like
4

Thanks for seeing this through and finding a solution. If you think there’s something to improve here, including the documentation, let me know.

I don’t think your premise was wrong, but I’m not sure I understand the exact issue you were facing. Namely, you should be able to see the output of format/2 in Sweep top-level buffers without specifying user_output as the output stream. I get:

?- format("Node was: ~k~n",[foo]).
Node was: foo
true.