/*************************************************************************

    File: readLine.pl
    Copyright (C) 2004 Patrick Blackburn & Johan Bos

    This file is part of BB2, version 1.0 (June 2004).

    BB2 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.

    BB2 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 General Public License
    along with BB2; if not, write to the Free Software Foundation, Inc., 
    59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*************************************************************************/

:- module(readLine,[readLine/1]).


/*========================================================================
   Output prompt, read from standard input and convert into list
========================================================================*/

readLine(WordList):-
   nl, write('> '),
   readWords(Words),
   checkWords(Words,WordList).


/*========================================================================
   Read in a sequence of characters, until a return is registered
========================================================================*/

readWords([Word|Rest]):-
   get0(Char),
   readWord(Char,Chars,State),
   name(Word,Chars),
   readRest(Rest,State).

readRest([],ended).

readRest(Rest,notended):-
   readWords(Rest).


/*========================================================================
   Read a word coded as Chars (a list of ascii values), starting 
   with with ascii value Char, and determine the State of input
   (`ended' = end of line, `notended' = not end of line).
   Blanks and full stops split words, a return ends a line.
========================================================================*/

readWord(32,[],notended):-!.     %%% blank

readWord(46,[],notended):-!.     %%% full stop

readWord(10,[],ended):-!.        %%% return

readWord(Code,[Code|Rest],State):-
   get0(Char),
   readWord(Char,Rest,State).


/*========================================================================
   Check if all words are unquoted atoms, if not convert them into atoms.
========================================================================*/

checkWords([],[]):- !.

checkWords([''|Rest1],Rest2):-
   checkWords(Rest1,Rest2).

checkWords([Atom|Rest1],[Atom2|Rest2]):-
   name(Atom,Word1),
   convertWord(Word1,Word2),
   name(Atom2,Word2),
   checkWords(Rest1,Rest2).


/*========================================================================
   Convert upper into lower case characters, and eliminate
   non-alphabetic characters.
========================================================================*/

convertWord([],[]):- !.

convertWord([Capital|Rest1],[Small|Rest2]):-
   Capital > 64, Capital < 91, !,
   Small is Capital + 32,
   convertWord(Rest1,Rest2).

convertWord([Number|Rest1],[Number|Rest2]):-
   Number > 47, Number < 58, !,
   convertWord(Rest1,Rest2).

convertWord([Weird|Rest1],Rest2):-
   (Weird < 97; Weird > 122), !,
   convertWord(Rest1,Rest2).

convertWord([Char|Rest1],[Char|Rest2]):-
   convertWord(Rest1,Rest2).