1/*  Part of XPCE --- The SWI-Prolog GUI toolkit
    2
    3    Author:        Jan Wielemaker and Anjo Anjewierden
    4    E-mail:        jan@swi.psy.uva.nl
    5    WWW:           http://www.swi.psy.uva.nl/projects/xpce/
    6    Copyright (c)  1985-2002, University of Amsterdam
    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
   11    are 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 OWNER 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%-----------------------------------------------
   36%   Module Definitions
   37%-----------------------------------------------
   38
   39:- module(scan_arguments,
   40        [ scan_arguments/2      % Arguments x ValueList
   41        , scan_arguments/3      % Arguments x ValueList -> Rest
   42        ]).   43
   44:- use_module(library(pce)).   45:- require([ select/3
   46           ]).   47
   48
   49%-----------------------------------------------
   50%   Scan Arguments
   51%-----------------------------------------------

scan_arguments/2 is used to scan a list of arguments and assign values to variables. Args is a list of instantiated arguments provided by the caller, the second argument contains name/value pairs where the value is unified with the value given in Args. The version Name=Value/Default allows Name to be omitted in Args and still bind Default to Value.

scan_arguments/3 is equivalent to scan_arguments/2, but unprocessed arguments are bound to `Rest' instead of printing an error message.

Error messages are printed on missing arguments.

?- scan_arguments([hello=world], [hello=X])

X = world

?- scan_arguments([name=anjo], [name=N, city=C/amsterdam]).

N = anjo
C = amsterdam

   77scan_arguments(Args, List, Rest) :-
   78    get_arguments(List, Args, Rest).
   79
   80scan_arguments(Args, List) :-
   81    get_arguments(List, Args, Rest),
   82    (   Rest == []
   83    ->  true
   84    ;   format(user_error,
   85               'scan_arguments:Arguments not required: ~w~n', Rest)
   86    ).
   87
   88get_arguments([], Args, Args) :- !.
   89get_arguments([Name = Value|T], Args, RestArgs) :-
   90    non_default_argument(Value),
   91    !,
   92    (   select(Name=Value, Args, Rest)
   93    ->  get_arguments(T, Rest, RestArgs)
   94    ;   format(user_error,
   95               'Argument ~w not present and no default defined', [Name])
   96    ).
   97get_arguments([Name = Value / Default|T], Args, RestArgs) :-
   98    (   select(Name=Value, Args, Rest)
   99    ->  get_arguments(T, Rest, RestArgs)
  100    ;   Value = Default,
  101        get_arguments(T, Args, RestArgs)
  102    ).
  103
  104
  105non_default_argument(Value) :- var(Value), !.
  106non_default_argument(_/_) :- !, fail.
  107non_default_argument(_)