/* $Id$
Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: wielemak@science.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2007, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(dcg_basics,
[ white//0, % <white inside line>
whites//0, % <white inside line>*
blank//0, % <blank>
blanks//0, % <blank>*
nonblank//1, % <nonblank>
nonblanks//1, % <nonblank>* --> chars (long)
blanks_to_nl//0, % [space,tab,ret]*nl
string//1, % <any>* -->chars (short)
string_without//2, % Exclude, -->chars (long)
% Characters
alpha_to_lower//1, % Get lower|upper, return lower
% Decimal numbers
digits//1, % [0-9]* -->chars
digit//1, % [0-9] --> char
integer//1, % [+-][0-9]+ --> integer
float//1, % [+-]?[0-9]+(.[0-9]*)?(e[+-]?[0-9]+)? --> float
number//1, % integer | float
% Hexadecimal numbers
xdigits//1, % [0-9a-f]* --> 0-15*
xdigit//1, % [0-9a-f] --> 0-15
xinteger//1, % [0-9a-f]+ --> integer
% Misc
eos//0, % demand end-of-string
% generation (TBD)
atom//1 % generate atom
]).
:- use_module(library(lists)).
/** <module> Various general DCG utilities
This library provides various commonly used DCG primitives acting on
list of character codes. Character classification is based on
code_type/2.
@tbd Try to achieve an accepted standard and move this into the
general SWI-Prolog library. None of this is HTTP specific.
*/
%% string_without(+End, -Codes)// is det.
%
% Take as many tokens from the input until the next token appears
% in End. End itself is left on the input. Typical use is to read
% upto a defined delimiter such as a newline or other reserved
% character.
%
% @see string//1.
string_without(Not, [C|T]) -->
[C],
{ \+ memberchk(C, Not)
}, !,
string_without(Not, T).
string_without(_, []) -->
[].
%% string(-Codes)// is nondet.
%
% Take as few as possible tokens from the input, taking one more
% each time on backtracking. This code is normally followed by a
% test for a delimiter. E.g.
%
% ==
% upto_colon(Atom) -->
% string(Codes), ":", !,
% { atom_codes(Atom, Codes) }.
% ==
string([]) -->
[].
string([H|T]) -->
[H],
string(T).
%% blanks// is det.
%
% Skip zero or more white-space characters.
blanks -->
blank, !,
blanks.
blanks -->
[].
%% blank// is semidet.
%
% Take next =space= character from input. Space characters include
% newline.
%
% @see white//0
blank -->
[C],
{ nonvar(C),
code_type(C, space)
}.
%% nonblanks(-Codes)// is det.
%
% Take all =graph= characters
nonblanks([H|T]) -->
[H],
{ code_type(H, graph)
}, !,
nonblanks(T).
nonblanks([]) -->
[].
%% nonblank(-Code)// is semidet.
%
% Code is the next non-blank (=graph=) character.
nonblank(H) -->
[H],
{ code_type(H, graph)
}.
%% blanks_to_nl// is semidet.
%
% Take a sequence of blank//0 codes if banks are followed by a
% newline or end of the input.
blanks_to_nl -->
"\n", !.
blanks_to_nl -->
blank, !,
blanks_to_nl.
blanks_to_nl -->
eos.
%% whites// is det.
%
% Skip white space _inside_ a line.
%
% @see blanks//0 also skips newlines.
whites -->
white, !,
whites.
whites -->
[].
%% white// is semidet.
%
% Take next =white= character from input. White characters do
% _not_ include newline.
white -->
[C],
{ nonvar(C),
code_type(C, white)
}.
/*******************************
* CHARACTER STUFF *
*******************************/
%% alpha_to_lower(+C)// is det.
%% alpha_to_lower(-C)// is semidet.
%
% Read a letter (class =alpha=) and return it as a lowercase
% letter. In output mode this simply emits the character.
alpha_to_lower(L) -->
{ integer(L) }, !,
[L].
alpha_to_lower(L) -->
[C],
{ code_type(C, alpha),
code_type(C, to_upper(L))
}.
/*******************************
* NUMBERS *
*******************************/
%% digits(?Chars)// is det.
%% digit(?Char)// is det.
%% integer(?Integer)// is det.
%
% Number processing. The predicate digits//1 matches a posibly
% empty set of digits, digit//1 processes a single digit and
% integer processes an optional sign followed by a non-empty
% sequence of digits into an integer.
digits([H|T]) -->
digit(H), !,
digits(T).
digits([]) -->
[].
digit(C) -->
[C],
{ code_type(C, digit)
}.
integer(I, Head, Tail) :-
integer(I), !,
format(codes(Head, Tail), '~w', [I]).
integer(I) -->
int_codes(Codes),
{ number_codes(I, Codes)
}.
int_codes([C,D0|D]) -->
sign(C), !,
digit(D0),
digits(D).
int_codes([D0|D]) -->
digit(D0),
digits(D).
%% float(?Float)// is det.
%
% Process a floating point number. The actual conversion is
% controlled by number_codes/2.
float(F, Head, Tail) :-
float(F), !,
with_output_to(codes(Head, Tail), write(F)).
float(F) -->
number(F),
{ float(F) }.
%% number(+Number)// is det.
%% number(-Number)// is semidet.
%
% Generate extract a number. Handles both integers and floating
% point numbers.
number(N, Head, Tail) :-
number(N), !,
format(codes(Head, Tail), '~w', N).
number(N) -->
int_codes(I),
( dot,
digit(DF0),
digits(DF)
-> {F = [0'., DF0|DF]}
; {F = ""}
),
( exp
-> int_codes(DI),
{E=[0'e|DI]}
; {E = ""}
),
{ append([I, F, E], Codes),
number_codes(N, Codes)
}.
sign(0'-) --> "-".
sign(0'+) --> "+".
dot --> ".".
exp --> "e".
exp --> "E".
/*******************************
* HEX NUMBERS *
*******************************/
%% xinteger(+Integer)// is det.
%% xinteger(-Integer)// is semidet.
%
% Generate or extract an integer from a sequence of hexadecimal
% digits.
xinteger(Val, Head, Tail) :-
integer(Val),
format(codes(Head, Tail), '~16r', [Val]).
xinteger(Val) -->
xdigit(D0),
xdigits(D),
{ mkval([D0|D], 16, Val)
}.
%% xdigit(-Weight)// is semidet.
%
% True if the next code is a hexdecimal digit with Weight. Weight
% is between 0 and 15.
xdigit(D) -->
[C],
{ code_type(C, xdigit(D))
}.
%% xdigits(-WeightList)// is det.
%
% List of weights of a sequence of hexadecimal codes. WeightList
% may be empty.
xdigits([D0|D]) -->
xdigit(D0), !,
xdigits(D).
xdigits([]) -->
[].
mkval([W0|Weights], Base, Val) :-
mkval(Weights, Base, W0, Val).
mkval([], _, W, W).
mkval([H|T], Base, W0, W) :-
W1 is W0*Base+H,
mkval(T, Base, W1, W).
/*******************************
* END-OF-STRING *
*******************************/
%% eos//
%
% True if at end of input list.
eos([], []).
/*******************************
* GENERATION *
*******************************/
%% atom(+Atom)// is det.
%
% Generate codes of Atom. Current implementation uses write/1,
% dealing with any Prolog term.
atom(Atom, Head, Tail) :-
format(codes(Head, Tail), '~w', [Atom]).