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): 2013,2014, 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;
   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(prolog_format,
   36          [ format_spec/2,                      % +Format, -Spec
   37            format_spec//1,                     % -Spec
   38            format_types/2                      % +Format, -Types
   39          ]).   40:- use_module(library(dcg/basics), [eos//0, integer//1, string_without//2]).   41:- use_module(library(when), [when/2]).   42
   43/** <module> Analyse format specifications
   44
   45This library parses the format specification  used by format/1, format/2
   46and format/3. The parsed  specification  can   be  used  to validate the
   47consistency of the  format  string  and   the  provided  arguments.  For
   48example:
   49
   50  ==
   51  ?- format_types('~d bottles of beer', Types).
   52  Types = [integer].
   53  ==
   54
   55@tbd    The current implementation does not support format_predicate/2.
   56@see    http://www.swi-prolog.org/pack/list?p=format_spec
   57@author Michael Hendricks
   58*/
   59
   60%%  format_spec(+Format, -Spec:list) is semidet.
   61%
   62%   Parse a format string. Each element of Spec is one of the following:
   63%
   64%    * text(Text)
   65%    Text sent to the output as is
   66%    * escape(Num,Colon,Action)
   67%    A format escape. Num represents the optional numeric portion of
   68%    an esape. Colon represents the optional colon in an escape.
   69%    Action is an atom representing the action to be take by this
   70%    escape.
   71
   72format_spec(Format, Spec) :-
   73    when((ground(Format);ground(Codes)),text_codes(Format, Codes)),
   74    once(phrase(format_spec(Spec), Codes, [])).
   75
   76%%  format_spec(-Spec)//
   77%
   78%   DCG for parsing format  strings.  It   doesn't  yet  generate format
   79%   strings from a spec. See format_spec/2 for details.
   80
   81format_spec([]) -->
   82    eos.
   83format_spec([escape(Numeric,Modifier,Action)|Rest]) -->
   84    "~",
   85    numeric_argument(Numeric),
   86    modifier_argument(Modifier),
   87    action(Action),
   88    format_spec(Rest).
   89format_spec([text(String)|Rest]) -->
   90    { when((ground(String);ground(Codes)),string_codes(String, Codes)) },
   91    string_without("~", Codes),
   92    { Codes \= [] },
   93    format_spec(Rest).
   94
   95%%  format_types(+Format:text, -Types:list) is det.
   96%
   97%   True when Format requires an argument list   with  terms of the type
   98%   specified by Types. The  length  of  this   list  is  the  number of
   99%   arguments required. Each value of Types is   a  type as described by
  100%   error:has_type/2.
  101
  102format_types(Format, Types) :-
  103    format_spec(Format, Spec),
  104    spec_types(Spec, Types).
  105
  106%%  spec_types(+FormatSpec, -Types:list(type)) is det.
  107%
  108%   True if FormatSpec requires format/2  to   have  arguments of Types.
  109%   Each value of Types is a type as described by error:has_type/2. This
  110%   notion of types is compatible with library(mavis).
  111
  112spec_types(Spec, Types) :-
  113    phrase(spec_types(Spec), Types).
  114
  115spec_types([]) -->
  116    [].
  117spec_types([Item|Items]) -->
  118    item_types(Item),
  119    spec_types(Items).
  120
  121item_types(text(_)) -->
  122    [].
  123item_types(escape(Numeric,_,Action)) -->
  124    numeric_types(Numeric),
  125    action_types(Action).
  126
  127numeric_types(number(_)) -->
  128    [].
  129numeric_types(character(_)) -->
  130    [].
  131numeric_types(star) -->
  132    [number].
  133numeric_types(nothing) -->
  134    [].
  135
  136action_types(Action) -->
  137    { atom_codes(Action, [Code]) },
  138    { action_types(Code, Types) },
  139    phrase(Types).
  140
  141%% text_codes(Text:text, Codes:codes).
  142text_codes(Var, Codes) :-
  143    var(Var),
  144    !,
  145    string_codes(Var, Codes).
  146text_codes(Atom, Codes) :-
  147    atom(Atom),
  148    !,
  149    atom_codes(Atom, Codes).
  150text_codes(String, Codes) :-
  151    string(String),
  152    !,
  153    string_codes(String, Codes).
  154text_codes(Codes, Codes) :-
  155    is_of_type(codes, Codes).
  156
  157
  158numeric_argument(number(N)) -->
  159    integer(N).
  160numeric_argument(character(C)) -->
  161    "`",
  162    [C].
  163numeric_argument(star) -->
  164    "*".
  165numeric_argument(nothing) -->
  166    "".
  167
  168modifier_argument(colon) -->
  169    ":".
  170modifier_argument(no_colon) -->
  171    \+ ":".
  172
  173action(Action) -->
  174    [C],
  175    { is_action(C) },
  176    { atom_codes(Action, [C]) }.
  177
  178%%  is_action(+Action:integer) is semidet.
  179%%  is_action(-Action:integer) is multi.
  180%
  181%   True if Action is a valid   format/2  action character. Iterates all
  182%   acceptable action characters, if Action is unbound.
  183
  184is_action(Action) :-
  185    action_types(Action, _).
  186
  187%%  action_types(?Action:integer, ?Types:list(type))
  188%
  189%   True if Action consumes arguments matching   Types.  An action (like
  190%   `~`), which consumes no arguments, has `Types=[]`. For example,
  191%
  192%       ?- action_types(0'~, Types).
  193%       Types = [].
  194%       ?- action_types(0'a, Types).
  195%       Types = [atom].
  196
  197action_types(0'~, []).
  198action_types(0'a, [atom]).
  199action_types(0'c, [integer]).  % specifically, a code
  200action_types(0'd, [integer]).
  201action_types(0'D, [integer]).
  202action_types(0'e, [float]).
  203action_types(0'E, [float]).
  204action_types(0'f, [float]).
  205action_types(0'g, [float]).
  206action_types(0'G, [float]).
  207action_types(0'i, [any]).
  208action_types(0'I, [integer]).
  209action_types(0'k, [any]).
  210action_types(0'n, []).
  211action_types(0'N, []).
  212action_types(0'p, [any]).
  213action_types(0'q, [any]).
  214action_types(0'r, [integer]).
  215action_types(0'R, [integer]).
  216action_types(0's, [text]).
  217action_types(0'@, [callable]).
  218action_types(0't, []).
  219action_types(0'|, []).
  220action_types(0'+, []).
  221action_types(0'w, [any]).
  222action_types(0'W, [any, list])