/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2012-2021, University of Amsterdam VU University Amsterdam SWI-Prolog Solutions b.v. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module(dcg_basics, [ white//0, % whites//0, % * blank//0, % blanks//0, % * nonblank//1, % nonblanks//1, % * --> chars (long) blanks_to_nl//0, % [space,tab,ret]*nl string//1, % * -->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-Fa-f]* --> 0-15* xdigit//1, % [0-9A-Fa-f] --> 0-15 xinteger//1, % [0-9A-Fa-f]+ --> integer prolog_var_name//1, % Read a Prolog variable name eol//0, % End of line eos//0, % Test end of input. remainder//1, % -List % generation (TBD) atom//1 % generate atom ]). :- use_module(library(lists)). :- use_module(library(error)). /** 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. This module started its life as library(http/dcg_basics) to support the HTTP protocol. Since then, it was increasingly used in code that has no relation to HTTP and therefore this library was moved to the core library. @tbd This is just a starting point. We need a comprehensive set of generally useful DCG primitives. */ %% string_without(+EndCodes, -Codes)// is det. % % Take as many codes from the input until the next character code % appears in the list EndCodes. The terminating code itself is % left on the input. Typical use is to read upto a defined % delimiter such as a newline or other reserved character. For % example: % % == % ..., % string_without("\n", RestOfLine) % == % % @arg EndCodes is a list of character codes. % @see string//1. string_without(End, Codes) --> { string(End), !, string_codes(End, EndCodes) }, list_string_without(EndCodes, Codes). string_without(End, Codes) --> list_string_without(End, Codes). list_string_without(Not, [C|T]) --> [C], { \+ memberchk(C, Not) }, !, list_string_without(Not, T). list_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. For example: % % == % upto_colon(Atom) --> % string(Codes), ":", !, % { atom_codes(Atom, Codes) }. % == % % @see string_without//2. 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 blanks 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 semidet. % % Read a letter (class =alpha=) and return it as a lowercase % letter. If C is instantiated and the DCG list is already bound, % C must be =lower= and matches both a lower and uppercase letter. % If the output list is unbound, its first element is bound to C. % For example: % % == % ?- alpha_to_lower(0'a, `AB`, R). % R = [66]. % ?- alpha_to_lower(C, `AB`, R). % C = 97, R = [66]. % ?- alpha_to_lower(0'a, L, R). % L = [97|R]. % == alpha_to_lower(L) --> [C], { nonvar(C) -> code_type(C, alpha), code_type(C, to_upper(L)) ; L = C }. /******************************* * NUMBERS * *******************************/ %% digits(?Chars)// is det. %% digit(?Char)// is det. %% integer(?Integer)// is det. % % Number processing. The predicate digits//1 matches a possibly % 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) :- nonvar(I), !, format(codes(Head, Tail), '~d', [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) --> { var(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) }. number(N) --> { type_error(number, N) }. 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. Hexadecimal characters include both uppercase (A-F) and % lowercase (a-f) letters. The value may be preceded by a sign % (+/-) xinteger(Val, Head, Tail) :- integer(Val), !, format(codes(Head, Tail), '~16r', [Val]). xinteger(Val) --> sign(C), !, xdigit(D0), xdigits(D), { mkval([D0|D], 16, Val0), ( C == 0'- -> Val is -Val0 ; Val = Val0 ) }. 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. Hexadecimal characters include both % uppercase (A-F) and lowercase (a-f) letters. 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. Hexadecimal characters include both uppercase % (A-F) and lowercase (a-f) letters. 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 * *******************************/ %! eol// % % Matches end-of-line. Matching \r\n, \n or end of input (eos//0). eol --> "\n", !. eol --> "\r\n", !. eol --> eos. %% eos// % % Matches end-of-input. The implementation behaves as the % following portable implementation: % % == % eos --> call(eos_). % eos_([], []). % == % % @tbd This is a difficult concept and violates the _context free_ % property of DCGs. Explain the exact problems. eos([], []). %% remainder(-List)// % % Unify List with the remainder of the input. remainder(List, List, []). /******************************* * PROLOG SYNTAX * *******************************/ %% prolog_var_name(-Name:atom)// is semidet. % % Matches a Prolog variable name. Primarily intended to deal with % quasi quotations that embed Prolog variables. prolog_var_name(Name) --> [C0], { code_type(C0, prolog_var_start) }, !, prolog_id_cont(CL), { atom_codes(Name, [C0|CL]) }. prolog_id_cont([H|T]) --> [H], { code_type(H, prolog_identifier_continue) }, !, prolog_id_cont(T). prolog_id_cont([]) --> "". /******************************* * GENERATION * *******************************/ %% atom(++Atom)// is det. % % Generate codes of Atom. Current implementation uses write/1, % dealing with any Prolog term. Atom must be ground though. atom(Atom, Head, Tail) :- must_be(ground, Atom), format(codes(Head, Tail), '~w', [Atom]).