1/*  Part of SWI-Prolog
    2
    3    Author:        Michael Hendricks
    4    E-mail:        michael@ndrix.org
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (C): 2013,2020, Michael Hendricks
    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 are
   11    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 HOLDER 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;
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   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(prolog_format,
   36          [ format_spec/2,                      % +Format, -Spec
   37            format_spec//1,                     % -Spec
   38            format_types/2                      % +Format, -Types
   39          ]).   40:- autoload(library(error),[existence_error/2]).   41:- autoload(library(dcg/basics),[eos//0,string_without//2,integer//1]).

?- format_types('~d bottles of beer', Types).
Types = [integer].

 format_spec(+Format, -Spec:list) is det

Parse a format string. Each element of Spec is one of the following:

text(Text)

Text sent to the output as is

escape(Num, Colon, Action)

A format escape. Num represents the optional numeric portion of an esape. Colon represents the optional colon in an escape. Action is an atom representing the action to be take by this escape.

   73format_spec(Format, Spec) :-
   74    (   is_list(Format)
   75    ->  Codes = Format
   76    ;   string_codes(Format, Codes)
   77    ),
   78    phrase(format_spec(Spec), Codes).

 format_spec(-Spec)// is det

DCG for parsing format strings. It doesn't yet generate format strings from a spec. See format_spec/2 for details.

   85format_spec([escape(Numeric,Modifier,Action)|Rest]) -->
   86    "~",
   87    !,
   88    numeric_argument(Numeric),
   89    modifier_argument(Modifier),
   90    action(Action),
   91    format_spec(Rest).
   92format_spec([text(String)|Rest]) -->
   93    string_without("~", Codes),
   94    { Codes \== [],
   95      !,
   96      string_codes(String, Codes)
   97    },
   98    format_spec(Rest).
   99format_spec([]) -->
  100    [].

 format_types(+Format:text, -Types:list) is det

True when Format requires an argument list with terms of the type specified by Types. The length of this list is the number of arguments required. Each value of Types is a type as described by error:has_type/2.

  109format_types(Format, Types) :-
  110    format_spec(Format, Spec),
  111    spec_types(Spec, Types).

 spec_types(+FormatSpec, -Types:list(type)) is det

True if FormatSpec requires format/2 to have arguments of Types. Each value of Types is a type as described by error:has_type/2. This notion of types is compatible with library(mavis).

  119spec_types(Spec, Types) :-
  120    phrase(spec_types(Spec), Types).
  121
  122spec_types([]) -->
  123    [].
  124spec_types([Item|Items]) -->
  125    item_types(Item),
  126    spec_types(Items).
  127
  128item_types(text(_)) -->
  129    [].
  130item_types(escape(Numeric,_,Action)) -->
  131    numeric_types(Numeric),
  132    action_types(Action).
  133
  134numeric_types(number(_)) -->
  135    [].
  136numeric_types(character(_)) -->
  137    [].
  138numeric_types(star) -->
  139    [number].
  140numeric_types(nothing) -->
  141    [].
  142
  143action_types(Action) -->
  144    { atom_codes(Action, [Code]) },
  145    { action_types(Code, Types) },
  146    phrase(Types).
  147
  148numeric_argument(number(N)) -->
  149    integer(N),
  150    !.
  151numeric_argument(character(C)) -->
  152    "`",
  153    !,
  154    [C].
  155numeric_argument(star) -->
  156    "*",
  157    !.
  158numeric_argument(nothing) -->
  159    "".
  160
  161modifier_argument(colon) -->
  162    ":".
  163modifier_argument(no_colon) -->
  164    \+ ":".
  165
  166action(Char) -->
  167    [C],
  168    { char_code(Char, C),
  169      (   is_action(C)
  170      ->  true
  171      ;   existence_error(format_character, Char)
  172      )
  173    }.

 is_action(+Action:integer) is semidet

is_action(-Action:integer) is multi

True if Action is a valid format/2 action character. Iterates all acceptable action characters, if Action is unbound.

  181is_action(Action) :-
  182    action_types(Action, _).

 action_types(?Action:integer, ?Types:list(type))

True if Action consumes arguments matching Types. An action (like ~), which consumes no arguments, has Types=[]. For example,

?- action_types(0'~, Types).
Types = [].
?- action_types(0'a, Types).
Types = [atom].

  194action_types(0'~, []).
  195action_types(0'a, [atom]).
  196action_types(0'c, [integer]).  % specifically, a code
  197action_types(0'd, [integer]).
  198action_types(0'D, [integer]).
  199action_types(0'e, [float]).
  200action_types(0'E, [float]).
  201action_types(0'f, [float]).
  202action_types(0'g, [float]).
  203action_types(0'G, [float]).
  204action_types(0'i, [any]).
  205action_types(0'I, [integer]).
  206action_types(0'k, [any]).
  207action_types(0'n, []).
  208action_types(0'N, []).
  209action_types(0'p, [any]).
  210action_types(0'q, [any]).
  211action_types(0'r, [integer]).
  212action_types(0'R, [integer]).
  213action_types(0's, [text]).
  214action_types(0'@, [callable]).
  215action_types(0't, []).
  216action_types(0'|, []).
  217action_types(0'+, []).
  218action_types(0'w, [any]).
  219action_types(0'W, [any, list])