(*  Title:      Pure/Thy/rail.ML

     Author:     Michael Kerscher, TU München

     Author:     Makarius

 Railroad diagrams in LaTeX.

 *)

 structure Rail: sig end =

 struct

 (** lexical syntax **)

 (* datatype token *)

 datatype kind = Keyword | Ident | String | EOF;

 datatype token = Token of Position.range * (kind * string);

 fun pos_of (Token ((pos, _), _)) = pos;

 fun end_pos_of (Token ((_, pos), _)) = pos;

 fun kind_of (Token (_, (k, _))) = k;

 fun content_of (Token (_, (_, x))) = x;

 (* diagnostics *)

 val print_kind =

  fn Keyword => "rail keyword"

   | Ident => "identifier"

   | String => "single-quoted string"

   | EOF => "end-of-file";

 fun print (Token ((pos, _), (k, x))) =

   (if k = EOF then print_kind k else print_kind k ^ " " ^ quote x) ^

   Position.str_of pos;

 fun print_keyword x = print_kind Keyword ^ " " ^ quote x;

 (* stopper *)

 fun mk_eof pos = Token ((pos, Position.none), (EOF, ""));

 val eof = mk_eof Position.none;

 fun is_eof (Token (_, (EOF, _))) = true

   | is_eof _ = false;

 val stopper =

   Scan.stopper (fn [] => eof | toks => mk_eof (end_pos_of (List.last toks))) is_eof;

 (* tokenize *)

 local

 fun token k ss = [Token (Symbol_Pos.range ss, (k, Symbol_Pos.content ss))];

 val scan_space = Scan.many1 (Symbol.is_blank o Symbol_Pos.symbol);

 val scan_keyword =

   Scan.one (member (op =) ["|", "*", "+", "?", "(", ")", "\\", ";", ":"] o Symbol_Pos.symbol);

 val scan_token =

   scan_space >> K [] ||

   scan_keyword >> (token Keyword o single) ||

   Lexicon.scan_id >> token Ident ||

   Symbol_Pos.scan_string_q >> (token String o #1 o #2);

 val scan =

   (Scan.repeat scan_token >> flat) --|

     Symbol_Pos.!!! "Rail lexical error: bad input"

       (Scan.ahead (Scan.one Symbol_Pos.is_eof));

 in

 fun tokenize text =

   #1 (Scan.error (Scan.finite Symbol_Pos.stopper scan) (Symbol_Pos.explode text));

 end;

 (** parsing **)

 fun !!! scan =

   let

     val prefix = "Rail syntax error";

     fun get_pos [] = " (past end-of-file!)"

       | get_pos (tok :: _) = Position.str_of (pos_of tok);

     fun err (toks, NONE) = prefix ^ get_pos toks

       | err (toks, SOME msg) =

           if String.isPrefix prefix msg then msg

           else prefix ^ get_pos toks ^ ": " ^ msg;

   in Scan.!! err scan end;

 fun $$$ x =

   Scan.one (fn tok => kind_of tok = Keyword andalso content_of tok = x) ||

   Scan.fail_with

     (fn [] => print_keyword x ^ " expected (past end-of-file!)"

       | tok :: _ => print_keyword x ^ " expected,\nbut " ^ print tok ^ " was found");

 fun enum1 sep scan = scan ::: Scan.repeat ($$$ sep |-- !!! scan);

 fun enum sep scan = enum1 sep scan || Scan.succeed [];

 fun parse_token kind =

   Scan.some (fn tok => if kind_of tok = kind then SOME (content_of tok) else NONE);

 val ident = parse_token Ident;

 val string = parse_token String;

 (** rail expressions **)

 (* datatype *)

 datatype rails =

   Cat of int * rail list

 and rail =

   Bar of rails list |

   Plus of rails * rails |

   Newline of int |

   Nonterminal of string |

   Terminal of string;

 fun reverse_cat (Cat (y, rails)) = Cat (y, rev (map reverse rails))

 and reverse (Bar cats) = Bar (map reverse_cat cats)

   | reverse (Plus (cat1, cat2)) = Plus (reverse_cat cat1, reverse_cat cat2)

   | reverse x = x;

 fun cat rails = Cat (0, rails);

 val empty = cat [];

 fun is_empty (Cat (_, [])) = true | is_empty _ = false;

 fun is_newline (Newline _) = true | is_newline _ = false;

 fun bar [Cat (_, [rail])] = rail

   | bar cats = Bar cats;

 fun plus cat1 cat2 = Plus (cat1, reverse_cat cat2);

 fun star cat1 cat2 =

   if is_empty cat2 then plus empty cat1

   else bar [empty, cat [plus cat1 cat2]];

 fun maybe rail = bar [empty, cat [rail]];

 (* read *)

 local

 fun body x = (enum1 "|" body1 >> bar) x

 and body0 x = (enum "|" body1 >> bar) x

 and body1 x =

  (body2 :|-- (fn a =>

    $$$ "*" |-- !!! body4e >> (cat o single o star a) ||

    $$$ "+" |-- !!! body4e >> (cat o single o plus a) ||

    Scan.succeed a)) x

 and body2 x = (Scan.repeat1 body3 >> cat) x

 and body3 x = (body4 :|-- (fn a => $$$ "?" >> K (maybe a) || Scan.succeed a)) x

 and body4 x =

  ($$$ "(" |-- !!! (body0 --| $$$ ")") ||

   $$$ "\\" >> K (Newline 0) ||

   ident >> Nonterminal ||

   string >> Terminal) x

 and body4e x = (Scan.option body4 >> (cat o the_list)) x;

 val rule = ident -- ($$$ ":" |-- !!! body) || body >> pair "";

 val rules = enum1 ";" (Scan.option rule) >> map_filter I;

 in

 fun read text =

   (case Scan.error (Scan.finite stopper rules) (tokenize text) of

     (res, []) => res

   | (_, tok :: _) => error ("Malformed rail input: " ^ print tok));

 end;

 (* latex output *)

 local

 fun vertical_range_cat (Cat (_, rails)) y =

   let val (rails', (_, y')) =

     fold_map (fn rail => fn (y0, y') =>

       if is_newline rail then (Newline (y' + 1), (y' + 1, y' + 2))

       else

         let val (rail', y0') = vertical_range rail y0;

         in (rail', (y0, Int.max (y0', y'))) end) rails (y, y + 1)

   in (Cat (y, rails'), y') end

 and vertical_range (Bar cats) y =

       let val (cats', y') = fold_map vertical_range_cat cats y

       in (Bar cats', Int.max (y + 1, y')) end

   | vertical_range (Plus (cat1, cat2)) y =

       let val ([cat1', cat2'], y') = fold_map vertical_range_cat [cat1, cat2] y;

       in (Plus (cat1', cat2'), Int.max (y + 1, y')) end

   | vertical_range (Newline _) y = (Newline (y + 2), y + 3)

   | vertical_range atom y = (atom, y + 1);

 fun output_text s = "\\isa{" ^ Output.output s ^ "}";

 fun output_cat c (Cat (_, rails)) = outputs c rails

 and outputs c [rail] = output c rail

   | outputs _ rails = implode (map (output "") rails)

 and output _ (Bar []) = ""

   | output c (Bar [cat]) = output_cat c cat

   | output _ (Bar (cat :: cats)) =

       "\\rail@bar\n" ^ output_cat "" cat ^

       implode (map (fn Cat (y, rails) =>

           "\\rail@nextbar{" ^ string_of_int y ^ "}\n" ^ outputs "" rails) cats) ^

       "\\rail@endbar\n"

   | output c (Plus (cat, Cat (y, rails))) =

       "\\rail@plus\n" ^ output_cat c cat ^

       "\\rail@nextplus{" ^ string_of_int y ^ "}\n" ^ outputs "c" rails ^

       "\\rail@endplus\n"

   | output _ (Newline y) = "\\rail@cr{" ^ string_of_int y ^ "}\n"

   | output c (Nonterminal s) = "\\rail@" ^ c ^ "nont{" ^ output_text s ^ "}[]\n"

   | output c (Terminal s) = "\\rail@" ^ c ^ "term{" ^ output_text s ^ "}[]\n";

 fun output_rule (name, rail) =

   let val (rail', y') = vertical_range rail 0 in

     "\\rail@begin{" ^ string_of_int y' ^ "}{" ^ output_text name ^ "}\n" ^

     output "" rail' ^

     "\\rail@end\n"

   end;

 fun output_rules rules =

   "\\begin{railoutput}\n" ^

   implode (map output_rule rules) ^

   "\\end{railoutput}\n";

 in

 val _ =

   Thy_Output.antiquotation "rail" (Scan.lift (Parse.position Args.name))

     (fn _ => output_rules o read);

 end;

 end;