1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: jan@swi-prolog.org 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2022, SWI-Prolog Solutions b.v. 7 All rights reserved. 8 9 Redistribution and use in source and binary forms, with or without 10 modification, are permitted provided that the following conditions 11 are met: 12 13 1. Redistributions of source code must retain the above copyright 14 notice, this list of conditions and the following disclaimer. 15 16 2. Redistributions in binary form must reproduce the above copyright 17 notice, this list of conditions and the following disclaimer in 18 the documentation and/or other materials provided with the 19 distribution. 20 21 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 29 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 31 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 32 POSSIBILITY OF SUCH DAMAGE. 33*/ 34 35:- module(streams, 36 [ with_output_to/3 % ?Output, :Goal, +Options 37 ]). 38:- autoload(library(error), [must_be/2]). 39:- autoload(library(option), [option/2, option/3]). 40:- autoload(library(apply), [maplist/2, maplist/3]). 41 42:- meta_predicate with_output_to(, , ).
current_output, user_output and user_error) in the string
Output. Options processed:
[], causing the
predicate to call with_output_to/2. The only admissible
list elements are the alias names for the Prolog standard
streams. As current_output is always captured, the only
two values are user_output and user_errortrue, pretend the output is a terminal, causing messages
to use ANSI term escape sequences for color.For example, the following captures an error message. Note that we must catch and print the message inside Goal. If we do not do so the exception of Goal is simply propagated into the environment without binding Output.
?- with_output_to(string(Out),
catch(A is log(-1), E, print_message(error, E)),
[capture([user_error]), color(true)]).
Out = "\u001B[1;31mERROR: is/2: Arithmetic: \c
evaluation error: `undefined'\n\u001B[0m",
E = error(evaluation_error(undefined), context(system:(is)/2, _)).
83with_output_to(Output, Goal, []) => 84 with_output_to(Output, Goal). 85with_output_to(Output, Goal, Options) => 86 option(capture(Streams), Options, []), 87 must_be(list(oneof([user_output,user_error])), Streams), 88 with_output_to( 89 Output, 90 setup_call_cleanup( 91 output_state(State, Streams), 92 capture(Goal, Streams, Options), 93 restore_output(State, Streams))). 94 95capture(Goal, Streams, Options) :- 96 current_output(S), 97 ( option(color(true), Options) 98 -> set_stream(S, tty(true)) 99 ; true 100 ), 101 maplist(capture_output(S), Streams), 102 once(Goal), 103 maplist(flush_output, [current_output|Streams]). 104 105output_state(State, Streams) :- 106 maplist(stream_id, Streams, State). 107 108stream_id(Alias, Stream) :- 109 stream_property(Stream, alias(Alias)). 110 111restore_output(State, Streams) :- 112 maplist(restore_stream, Streams, State). 113 114restore_stream(Alias, Stream) :- 115 set_stream(Stream, alias(Alias)). 116 117capture_output(S, Alias) :- 118 set_stream(S, alias(Alias))
Manage Prolog streams
This library provides high level primitives for stream operations. It is related to the
charsio.plandcodesio.pllibraries. Considering these are de-facto standard Prolog libraries we prefer to leave these untouched.*/