src/Pure/Syntax/scan.ML
author wenzelm
Wed, 13 May 1998 12:20:28 +0200
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child 4924 cf6bb75968c4
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(*  Title:	Pure/Syntax/scan.ML
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    ID:		$Id$
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    Author:	Markus Wenzel and Tobias Nipkow, TU Muenchen
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Generic scanners (for potentially infinite input).
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*)
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infix 5 -- |-- --| ^^;
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infix 3 >>;
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infix 0 ||;
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signature BASIC_SCAN =
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sig
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  val !! : ('a * string option -> string) -> ('a -> 'b) -> 'a -> 'b
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  val >> : ('a -> 'b * 'c) * ('b -> 'd) -> 'a -> 'd * 'c
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  val || : ('a -> 'b) * ('a -> 'b) -> 'a -> 'b
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  val -- : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> ('b * 'd) * 'e
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  val |-- : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> 'd * 'e
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  val --| : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> 'b * 'e
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  val ^^ : ('a -> string * 'b) * ('b -> string * 'c) -> 'a -> string * 'c
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  val $$ : ''a -> ''a list -> ''a * ''a list
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end;
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signature SCAN =
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sig
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  include BASIC_SCAN
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  val fail: 'a -> 'b
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  val fail_with: ('a -> string) -> 'a -> 'b
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  val succeed: 'a -> 'b -> 'a * 'b
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  val one: ('a -> bool) -> 'a list -> 'a * 'a list
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  val any: ('a -> bool) -> 'a list -> 'a list * 'a list
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  val any1: ('a -> bool) -> 'a list -> 'a list * 'a list
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  val optional: ('a -> 'b * 'a) -> 'b -> 'a -> 'b * 'a
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  val option: ('a -> 'b * 'a) -> 'a -> 'b option * 'a
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  val repeat: ('a -> 'b * 'a) -> 'a -> 'b list * 'a
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  val repeat1: ('a -> 'b * 'a) -> 'a -> 'b list * 'a
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  val max: ('a * 'a -> bool) -> ('b -> 'a * 'b) -> ('b -> 'a * 'b) -> 'b -> 'a * 'b
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  val ahead: ('a -> 'b * 'c) -> 'a -> 'b * 'a
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  val depend: ('a -> 'b -> ('c * 'd) * 'e) -> 'a * 'b -> 'd * ('c * 'e)
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  val lift: ('a -> 'b * 'c) -> 'd * 'a -> 'b * ('d * 'c)
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  val pass: 'a -> ('a * 'b -> 'c * ('d * 'e)) -> 'b -> 'c * 'e
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  val try: ('a -> 'b) -> 'a -> 'b
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  val force: ('a -> 'b) -> 'a -> 'b
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  val prompt: string -> ('a -> 'b) -> 'a -> 'b
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  val finite': ''a -> ('b * ''a list -> 'c * ('d * ''a list))
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    -> 'b * ''a list -> 'c * ('d * ''a list)
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  val finite: ''a -> (''a list -> 'b * ''a list) -> ''a list -> 'b * ''a list
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  val error: ('a -> 'b) -> 'a -> 'b
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  val source: string -> (string -> 'a -> 'b list * 'a) ->
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    ('c * 'a -> 'd) -> ('e * 'b list -> 'f * ('g * 'c)) -> 'e * 'a -> 'f * ('g * 'd)
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  val bulk: bool -> ('a -> 'b * 'a) -> 'a -> 'b list * 'a
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  type lexicon
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  val dest_lexicon: lexicon -> string list list
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  val make_lexicon: string list list -> lexicon
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  val empty_lexicon: lexicon
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  val extend_lexicon: lexicon -> string list list -> lexicon
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  val merge_lexicons: lexicon -> lexicon -> lexicon
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  val literal: lexicon -> string list -> string list * string list
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end;
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structure Scan: SCAN =
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struct
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(** scanners **)
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exception MORE of string option;	(*need more input (use prompt)*)
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exception FAIL of string option;	(*try alternatives (reason of failure)*)
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exception ABORT of string;		(*dead end*)
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(* scanner combinators *)
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fun (scan >> f) xs = apfst f (scan xs);
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fun (scan1 || scan2) xs = scan1 xs handle FAIL _ => scan2 xs;
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fun (scan1 -- scan2) xs =
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  let
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    val (x, ys) = scan1 xs;
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    val (y, zs) = scan2 ys;
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  in ((x, y), zs) end;
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fun (scan1 |-- scan2) = scan1 -- scan2 >> #2;
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fun (scan1 --| scan2) = scan1 -- scan2 >> #1;
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fun (scan1 ^^ scan2) = scan1 -- scan2 >> op ^;
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(* generic scanners *)
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fun fail _ = raise FAIL None;
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fun fail_with msg_of xs = raise FAIL (Some (msg_of xs));
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fun succeed y xs = (y, xs);
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fun one _ [] = raise MORE None
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  | one pred (x :: xs) =
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      if pred x then (x, xs) else raise FAIL None;
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fun $$ _ [] = raise MORE None
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  | $$ a (x :: xs) =
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      if a = x then (x, xs) else raise FAIL None;
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fun any _ [] = raise MORE None
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  | any pred (lst as x :: xs) =
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      if pred x then apfst (cons x) (any pred xs)
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      else ([], lst);
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fun any1 pred = one pred -- any pred >> op ::;
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fun optional scan def = scan || succeed def;
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fun option scan = optional (scan >> Some) None;
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fun repeat scan xs = (scan -- repeat scan >> op :: || succeed []) xs;
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fun repeat1 scan = scan -- repeat scan >> op ::;
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fun max leq scan1 scan2 xs =
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  (case (option scan1 xs, option scan2 xs) of
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    ((None, _), (None, _)) => raise FAIL None		(*looses FAIL msg!*)
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  | ((Some tok1, xs'), (None, _)) => (tok1, xs')
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  | ((None, _), (Some tok2, xs')) => (tok2, xs')
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  | ((Some tok1, xs1'), (Some tok2, xs2')) =>
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      if leq (tok2, tok1) then (tok1, xs1') else (tok2, xs2'));
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fun ahead scan xs = (fst (scan xs), xs);
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(* state based scanners *)
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fun depend scan (st, xs) =
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  let val ((st', y), xs') = scan st xs
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  in (y, (st', xs')) end;
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fun lift scan (st, xs) =
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  let val (y, xs') = scan xs
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  in (y, (st, xs')) end;
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fun pass st scan xs =
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  let val (y, (_, xs')) = scan (st, xs)
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  in (y, xs') end;
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(* exception handling *)
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fun !! err scan xs = scan xs handle FAIL msg => raise ABORT (err (xs, msg));
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fun try scan xs = scan xs handle MORE _ => raise FAIL None | ABORT _ => raise FAIL None;
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fun force scan xs = scan xs handle MORE _ => raise FAIL None;
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fun prompt str scan xs = scan xs handle MORE None => raise MORE (Some str);
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fun error scan xs = scan xs handle ABORT msg => Library.error msg;
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(* finite scans *)
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fun finite' stopper scan (state, input) =
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  let
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    fun lost () = raise ABORT "Scanner bug: lost stopper of finite scan!";
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    fun stop [] = lost ()
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      | stop lst =
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          let val (xs, x) = split_last lst
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          in if x = stopper then ((), xs) else lost () end;
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  in
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    if exists (equal stopper) input then
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      raise ABORT "Stopper may not occur in input of finite scan!"
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    else (force scan --| lift stop) (state, input @ [stopper])
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  end;
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fun finite stopper scan xs =
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  let val (y, ((), xs')) = finite' stopper (lift scan) ((), xs)
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  in (y, xs') end;
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(* infinite scans -- draining state-based source *)
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fun source def_prmpt get unget scan (state, src) =
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  let
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    fun drain (xs, s) =
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      (scan (state, xs), s)
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        handle MORE prmpt =>
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          let val (xs', s') = get (if_none prmpt def_prmpt) s in
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            if null xs' then raise ABORT "Input source exhausted"
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            else drain (xs @ xs', s')
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          end;
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    val ((ys, (state', rest)), src') = drain (get def_prmpt src);
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  in (ys, (state', unget (rest, src'))) end;
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fun single scan = scan >> (fn x => [x]);
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fun many scan = scan -- repeat (try scan) >> (op ::);
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fun bulk do_many = if do_many then many else single;
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(** datatype lexicon **)
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datatype lexicon =
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  Empty |
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  Branch of string * string list * lexicon * lexicon * lexicon;
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val no_literal = [];
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(* dest_lexicon *)
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fun dest_lexicon Empty = []
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  | dest_lexicon (Branch (_, [], lt, eq, gt)) =
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      dest_lexicon lt @ dest_lexicon eq @ dest_lexicon gt
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  | dest_lexicon (Branch (_, cs, lt, eq, gt)) =
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      dest_lexicon lt @ [cs] @ dest_lexicon eq @ dest_lexicon gt;
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(* empty, extend, make, merge lexicons *)
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val empty_lexicon = Empty;
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fun extend_lexicon lexicon chrss =
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  let
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    fun ext (lex, chrs) =
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      let
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	fun add (Branch (d, a, lt, eq, gt)) (chs as c :: cs) =
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	      if c < d then Branch (d, a, add lt chs, eq, gt)
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	      else if c > d then Branch (d, a, lt, eq, add gt chs)
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	      else Branch (d, if null cs then chrs else a, lt, add eq cs, gt)
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	  | add Empty [c] =
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	      Branch (c, chrs, Empty, Empty, Empty)
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	  | add Empty (c :: cs) =
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	      Branch (c, no_literal, Empty, add Empty cs, Empty)
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	  | add lex [] = lex;
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      in add lex chrs end;
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  in foldl ext (lexicon, chrss \\ dest_lexicon lexicon) end;
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val make_lexicon = extend_lexicon empty_lexicon;
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fun merge_lexicons lex1 lex2 =
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  let
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    val chss1 = dest_lexicon lex1;
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    val chss2 = dest_lexicon lex2;
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  in
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    if chss2 subset chss1 then lex1
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    else if chss1 subset chss2 then lex2
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    else extend_lexicon lex1 chss2
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  end;
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(* scan literal *)
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fun literal lex chrs =
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  let
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    fun lit Empty res _ = res
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      | lit (Branch _) _ [] = raise MORE None
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      | lit (Branch (d, a, lt, eq, gt)) res (chs as c :: cs) =
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	  if c < d then lit lt res chs
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	  else if c > d then lit gt res chs
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	  else lit eq (if a = no_literal then res else Some (a, cs)) cs;
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  in
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    (case lit lex None chrs of
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      None => raise FAIL None
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    | Some res => res)
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  end;
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end;
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structure BasicScan: BASIC_SCAN = Scan;
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open BasicScan;