(*  Title:      Pure/General/xml.ML

    ID:         $Id$

    Author:     David Aspinall, Stefan Berghofer and Markus Wenzel

    License:    GPL (GNU GENERAL PUBLIC LICENSE)

Basic support for XML.

*)

signature XML =

sig

  val header: string

  val text: string -> string

  val cdata: string -> string

  val element: string -> (string * string) list -> string list -> string

  datatype tree =

      Elem of string * (string * string) list * tree list

    | Text of string

  val string_of_tree: tree -> string

  val parse_content: string list -> tree list * string list

  val parse_elem: string list -> tree * string list

  val parse_document: string list -> (string option * tree) * string list

  val tree_of_string: string -> tree

end;

structure XML: XML =

struct

(** string based representation (small scale) **)

val header = "<?xml version=\"1.0\"?>\n";

(* text and character data *)

fun decode "&lt;" = "<"

  | decode ">" = ">"

  | decode "&" = "&"

  | decode "'" = "'"

  | decode """ = "\""

  | decode c = c;

fun encode "<" = "&lt;"

  | encode ">" = ">"

  | encode "&" = "&"

  | encode "'" = "'"

  | encode "\"" = """

  | encode c = c;

val text = Library.translate_string encode;

val cdata = enclose "<![CDATA[" "]]>";

(* elements *)

fun attribute (a, x) = a ^ " = \"" ^ text x ^ "\"";

fun element name atts cs =

  let val elem = space_implode " " (name :: map attribute atts) in

    if null cs then enclose "<" "/>" elem

    else enclose "<" ">" elem ^ implode cs ^ enclose "</" ">" name

  end;

(** explicit XML trees **)

datatype tree =

    Elem of string * (string * string) list * tree list

  | Text of string;

fun string_of_tree tree =

  let

    fun string_of (Elem (name, atts, ts)) buf =

        let val buf' =

          buf |> Buffer.add "<"

          |> fold Buffer.add (separate " " (name :: map attribute atts))

        in

          if null ts then

            buf' |> Buffer.add "/>"

          else

            buf' |> Buffer.add ">"

            |> fold string_of ts

            |> Buffer.add "</" |> Buffer.add name |> Buffer.add ">"

        end

      | string_of (Text s) buf = Buffer.add (text s) buf;

  in Buffer.content (string_of tree Buffer.empty) end;

(** XML parsing **)

fun err s (xs, _) =

  "XML parsing error: " ^ s ^ "\nfound: " ^ quote (Symbol.beginning 100 xs);

val scan_whspc = Scan.any Symbol.is_blank;

val scan_special = $$ "&" ^^ Symbol.scan_id ^^ $$ ";" >> decode;

val parse_chars = Scan.repeat1 (Scan.unless (scan_whspc -- $$ "<")

  (scan_special || Scan.one Symbol.not_eof)) >> implode;

val parse_cdata = Scan.this_string "<![CDATA[" |--

  (Scan.repeat (Scan.unless (Scan.this_string "]]>") (Scan.one Symbol.not_eof)) >>

    implode) --| Scan.this_string "]]>";

val parse_att =

  Symbol.scan_id --| scan_whspc --| $$ "=" --| scan_whspc --

  (($$ "\"" || $$ "'") :-- (fn s => (Scan.repeat (Scan.unless ($$ s)

    (scan_special || Scan.one Symbol.not_eof)) >> implode) --| $$ s) >> snd);

val parse_comment = Scan.this_string "<!--" --

  Scan.repeat (Scan.unless (Scan.this_string "-->") (Scan.one Symbol.not_eof)) --

  Scan.this_string "-->";

val parse_pi = Scan.this_string "<?" |--

  Scan.repeat (Scan.unless (Scan.this_string "?>") (Scan.one Symbol.not_eof)) --|

  Scan.this_string "?>";

fun parse_content xs =

  ((Scan.optional (scan_whspc |-- parse_chars >> (single o Text)) [] --

    (Scan.repeat (scan_whspc |--

       (   parse_elem >> single

        || parse_cdata >> (single o Text)

        || parse_pi >> K []

        || parse_comment >> K []) --

       Scan.optional (scan_whspc |-- parse_chars >> (single o Text)) []

         >> op @) >> flat) >> op @) --| scan_whspc) xs

and parse_elem xs =

  ($$ "<" |-- Symbol.scan_id --

    Scan.repeat (scan_whspc |-- parse_att) --| scan_whspc :-- (fn (s, _) =>

      !! (err "Expected > or />")

        (Scan.this_string "/>" >> K []

         || $$ ">" |-- parse_content --|

            !! (err ("Expected </" ^ s ^ ">"))

              (Scan.this_string ("</" ^ s) --| scan_whspc --| $$ ">"))) >>

    (fn ((s, atts), ts) => Elem (s, atts, ts))) xs;

val parse_document =

  Scan.option (Scan.this_string "<!DOCTYPE" -- scan_whspc |--

    (Scan.repeat (Scan.unless ($$ ">")

      (Scan.one Symbol.not_eof)) >> implode) --| $$ ">" --| scan_whspc) --

  parse_elem;

fun tree_of_string s =

  (case Scan.finite Symbol.stopper (Scan.error (!! (err "Malformed element")

      (scan_whspc |-- parse_elem --| scan_whspc))) (Symbol.explode s) of

    (x, []) => x

  | (_, ys) => error ("XML parsing error: Unprocessed input\n" ^ Symbol.beginning 100 ys));

end;