1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2009-2023, University of Amsterdam 7 CWI, Amsterdam 8 SWI-Prolog Solutions b.v. 9 All rights reserved. 10 11 Redistribution and use in source and binary forms, with or without 12 modification, are permitted provided that the following conditions 13 are met: 14 15 1. Redistributions of source code must retain the above copyright 16 notice, this list of conditions and the following disclaimer. 17 18 2. Redistributions in binary form must reproduce the above copyright 19 notice, this list of conditions and the following disclaimer in 20 the documentation and/or other materials provided with the 21 distribution. 22 23 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 24 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 25 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 26 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 27 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 28 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 29 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 30 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 31 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 33 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 34 POSSIBILITY OF SUCH DAMAGE. 35*/ 36 37:- module(portray_text, 38 [ portray_text/1, % +Bool 39 set_portray_text/2, % +Name, +Value 40 set_portray_text/3 % +Name, ?Old, +Value 41 ]). 42:- autoload(library(error), [must_be/2, domain_error/2]). 43 44:- multifile 45 is_text_code/1. % +Integer

Portray text

SWI-Prolog has the special string data type. However, in Prolog, text may be represented more traditionally as a list of character-codes, i.e. (small) integers (in SWI-Prolog specifically, those are Unicode code points). This results in output like the following (here using the backquote notation which maps text to a list of codes):

?- writeln(`hello`).
[104, 101, 108, 108, 111]

?- atom_codes("hello",X).
X = [104,101,108,108,111].

Unless you know the Unicode tables by heart, this is pretty unpleasant for debugging. Loading library(portray_text) makes the toplevel and debugger consider certain lists of integers as text and print them as text. This is called "portraying". Of course, interpretation is imperfect as there is no way to tell in general whether [65,66] should written as `AB` or as [65,66]. Therefore it is important that the user be aware of the fact that this conversion is enabled. This is why this library must be loaded explicitly.

To be able to copy the printed representation and paste it back, printed text is enclosed in back quotes if current_prolog_flag/2 for the flag back_quotes is codes (the default), and enclosed in double quotes otherwise. Certain control characters are printed out in backslash-escaped form.

The default heuristic only considers list of codes as text if the codes are all from the set of 7-bit ASCII without most of the control characters. A code is classified as text by text_code/1, which in turn calls is_text_code/1. Define portray_text:is_text_code/1 to succeed on additional codes for more flexibility (by default, that predicate succeeds nowhere). For example:

?- maplist([C,R]>>(portray_text:text_code(C)->R=y;R=n),
           `G\u00e9n\u00e9rateur`,Results).
Results = [y,n,y,n,y,y,y,y,y,y].

Now make is_text_code/1 accept anything:

?- [user].
|: portray_text:is_text_code(_).
|: ^D
% user://3 compiled 0.00 sec, 1 clauses
true.

Then:

?- maplist([C,R]>>(portray_text:text_code(C)->R=y;R=n),
           `G\u00e9n\u00e9rateur`,Results).
Results = [y,y,y,y,y,y,y,y,y,y].

110:- dynamic 111 portray_text_option/2. 112 113portray_text_option(enabled, true). 114portray_text_option(min_length, 3). 115portray_text_option(ellipsis, 30). 116 117pt_option(enabled, boolean). 118pt_option(min_length, nonneg). 119pt_option(ellipsis, nonneg).

147set_portray_text(Key, New) :- 148 set_portray_text(Key, _, New). 149set_portray_text(Key, Old, New) :- 150 nonvar(Key), 151 pt_option(Key, Type), 152 !, 153 portray_text_option(Key, Old), 154 ( Old == New 155 -> true 156 ; must_be(Type, New), 157 retractall(portray_text_option(Key, _)), 158 assert(portray_text_option(Key, New)) 159 ). 160set_portray_text(Key, _, _) :- 161 domain_error(portray_text_option, Key). 162 163 164:- multifile 165 user:portray/1. 166:- dynamic 167 user:portray/1. 168 169user:portray(Codes) :- 170 portray_text_option(enabled, true), 171 '$skip_list'(Length, Codes, _Tail), 172 portray_text_option(min_length, MinLen), 173 Length >= MinLen, 174 mostly_codes(Codes, 0.9), 175 portray_text_option(ellipsis, IfLonger), 176 quote(C), 177 put_code(C), 178 ( Length > IfLonger 179 -> First is IfLonger - 5, 180 Skip is Length - 5, 181 skip_first(Skip, Codes, Rest), 182 put_n_codes(First, Codes, C), 183 format('...', []) 184 ; Rest = Codes 185 ), 186 put_var_codes(Rest, C), 187 put_code(C). 188 189quote(0'`) :- 190 current_prolog_flag(back_quotes, codes), 191 !. 192quote(0'"). 193 194put_n_codes(N, [H|T], C) :- 195 N > 0, 196 !, 197 emit_code(H, C), 198 N2 is N - 1, 199 put_n_codes(N2, T, C). 200put_n_codes(_, _, _). 201 202skip_first(N, [_|T0], T) :- 203 succ(N2, N), 204 !, 205 skip_first(N2, T0, T). 206skip_first(_, L, L). 207 208put_var_codes(Var, _) :- 209 var_or_numbered(Var), 210 !, 211 format('|~p', [Var]). 212put_var_codes([], _). 213put_var_codes([H|T], C) :- 214 emit_code(H, C), 215 put_var_codes(T, C). 216 217emit_code(Q, Q) :- !, format('\\~c', [Q]). 218emit_code(0'\b, _) :- !, format('\\b'). 219emit_code(0'\r, _) :- !, format('\\r'). 220emit_code(0'\n, _) :- !, format('\\n'). 221emit_code(0'\t, _) :- !, format('\\t'). 222emit_code(C, _) :- put_code(C). 223 224mostly_codes(Codes, MinFactor) :- 225 mostly_codes(Codes, 0, 0, MinFactor). 226 227mostly_codes(Var, _, _, _) :- 228 var_or_numbered(Var), 229 !. 230mostly_codes([], Yes, No, MinFactor) :- 231 Yes >= (Yes+No)*MinFactor. 232mostly_codes([H|T], Yes, No, MinFactor) :- 233 integer(H), 234 H >= 0, 235 H =< 0x1ffff, 236 ( text_code(H) 237 -> Yes1 is Yes+1, 238 mostly_codes(T, Yes1, No, MinFactor) 239 ; catch(code_type(H, print),error(_,_),fail), 240 No1 is No+1, 241 mostly_codes(T, Yes, No1, MinFactor), 242 ( Yes+No1 > 100 243 -> Yes >= (Yes+No1)*MinFactor 244 ; true 245 ) 246 ). 247 248% Idea: Maybe accept anything and hex-escape anything non-printable? 249% In particular, I could imaging 0 and ESC appearing in text of interest. 250% Currently we really accept only 7-bit ASCII so even latin-1 text 251% precludes recognition. 252% Bug?: emit_code/2 can emit backspace but backspace (8) is not accepted below 253 254text_code(Code) :- 255 is_text_code(Code), 256 !. 257text_code(9). % horizontal tab, \t 258text_code(10). % newline \n 259text_code(13). % carriage return \r 260text_code(C) :- % space to tilde (127 is DEL) 261 between(32, 126, C). 262 263var_or_numbered(Var) :- 264 var(Var), 265 !. 266var_or_numbered('$VAR'(_)).