% For number_codes/2 we want to just fail if the codes do not represent an integer.
% gprolog.html#number-atom%2F2
% > Number is a variable, Atom (or Chars or Codes) cannot be parsed as a number and the value of the syntax_error Prolog flag is error (section 8.22.1)
:- set_prolog_flag(syntax_error, fail).


joy_lex([tok(Token)|Ls]) --> chars(Token), !, joy_lex(Ls).
joy_lex([  lbracket|Ls]) --> "[",          !, joy_lex(Ls).
joy_lex([  rbracket|Ls]) --> "]",          !, joy_lex(Ls).

joy_lex(Ls) --> blank, !, joy_lex(Ls).

joy_lex([]) --> [].


% Then parse the tokens converting them to Prolog values and building up
% the list structures (if any.)

joy_parse([J|Js]) --> joy_term(J), !, joy_parse(Js).
joy_parse([]) --> [].

joy_term(list(J)) --> [lbracket], !, joy_parse(J), [rbracket].
joy_term(Token) --> [tok(Codes)], {joy_token(Token, Codes)}.

joy_token(int(I), Codes) :- write(Codes) ,number_codes(I, Codes), !.
joy_token(bool(true), "true") :- !.
joy_token(bool(false), "false") :- !.
joy_token(symbol(S), Codes) :- atom_codes(S, Codes).

text_to_expression(Text, Expression) :-
    phrase(joy_lex(Tokens), Text), !,
    phrase(joy_parse(Expression), Tokens).

% Apologies for all the (green, I hope) cuts.  The strength of the Joy
% syntax is that it's uninteresting.

chars([Ch|Rest]) --> char(Ch), chars(Rest).
chars([Ch])      --> char(Ch).

char(Ch) --> \+ blank, [Ch], { Ch \== 0'[, Ch \== 0'] }.


blank --> [9].
blank --> [10].
blank --> [11].
blank --> [12].
blank --> [13].
blank --> [32].
blank --> [194, 133].
blank --> [194, 160].
blank --> [225, 154, 128].
blank --> [226, 128, 128].
blank --> [226, 128, 129].
blank --> [226, 128, 130].
blank --> [226, 128, 131].
blank --> [226, 128, 132].
blank --> [226, 128, 133].
blank --> [226, 128, 134].
blank --> [226, 128, 135].
blank --> [226, 128, 136].
blank --> [226, 128, 137].
blank --> [226, 128, 138].
blank --> [226, 128, 168].
blank --> [226, 128, 169].
blank --> [226, 128, 175].
blank --> [226, 129, 159].
blank --> [227, 128, 128].