(*  Title:      Pure/General/scan.ML

     Author:     Markus Wenzel and Tobias Nipkow, TU Muenchen

 Generic scanners (for potentially infinite input).

 *)

 infix 5 -- :-- :|-- |-- --| ^^;

 infixr 5 ::: @@@;

 infix 3 >>;

 infixr 0 ||;

 signature BASIC_SCAN =

 sig

   type message = unit -> string

   (*error msg handler*)

   val !! : ('a * message option -> message) -> ('a -> 'b) -> 'a -> 'b

   (*apply function*)

   val >> : ('a -> 'b * 'c) * ('b -> 'd) -> 'a -> 'd * 'c

   (*alternative*)

   val || : ('a -> 'b) * ('a -> 'b) -> 'a -> 'b

   (*sequential pairing*)

   val -- : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> ('b * 'd) * 'e

   (*dependent pairing*)

   val :-- : ('a -> 'b * 'c) * ('b -> 'c -> 'd * 'e) -> 'a -> ('b * 'd) * 'e

   (*projections*)

   val :|-- : ('a -> 'b * 'c) * ('b -> 'c -> 'd * 'e) -> 'a -> 'd * 'e

   val |-- : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> 'd * 'e

   val --| : ('a -> 'b * 'c) * ('c -> 'd * 'e) -> 'a -> 'b * 'e

   (*concatenation*)

   val ^^ : ('a -> string * 'b) * ('b -> string * 'c) -> 'a -> string * 'c

   val ::: : ('a -> 'b * 'c) * ('c -> 'b list * 'd) -> 'a -> 'b list * 'd

   val @@@ : ('a -> 'b list * 'c) * ('c -> 'b list * 'd) -> 'a -> 'b list * 'd

   (*one element literal*)

   val $$ : string -> string list -> string * string list

   val ~$$ : string -> string list -> string * string list

 end;

 signature SCAN =

 sig

   include BASIC_SCAN

   val prompt: string -> ('a -> 'b) -> 'a -> 'b

   val permissive: ('a -> 'b) -> 'a -> 'b

   val error: ('a -> 'b) -> 'a -> 'b

   val catch: ('a -> 'b) -> 'a -> 'b    (*exception Fail*)

   val fail: 'a -> 'b

   val fail_with: ('a -> message) -> 'a -> 'b

   val succeed: 'a -> 'b -> 'a * 'b

   val some: ('a -> 'b option) -> 'a list -> 'b * 'a list

   val one: ('a -> bool) -> 'a list -> 'a * 'a list

   val this: string list -> string list -> string list * string list

   val this_string: string -> string list -> string * string list

   val many: ('a -> bool) -> 'a list -> 'a list * 'a list

   val many1: ('a -> bool) -> 'a list -> 'a list * 'a list

   val optional: ('a -> 'b * 'a) -> 'b -> 'a -> 'b * 'a

   val option: ('a -> 'b * 'a) -> 'a -> 'b option * 'a

   val repeat: ('a -> 'b * 'a) -> 'a -> 'b list * 'a

   val repeat1: ('a -> 'b * 'a) -> 'a -> 'b list * 'a

   val single: ('a -> 'b * 'a) -> 'a -> 'b list * 'a

   val bulk: ('a -> 'b * 'a) -> 'a -> 'b list * 'a

   val max: ('a * 'a -> bool) -> ('b -> 'a * 'b) -> ('b -> 'a * 'b) -> 'b -> 'a * 'b

   val ahead: ('a -> 'b * 'c) -> 'a -> 'b * 'a

   val unless: ('a -> 'b * 'a) -> ('a -> 'c * 'd) -> 'a -> 'c * 'd

   val first: ('a -> 'b) list -> 'a -> 'b

   val state: 'a * 'b -> 'a * ('a * 'b)

   val depend: ('a -> 'b -> ('c * 'd) * 'e) -> 'a * 'b -> 'd * ('c * 'e)

   val peek: ('a -> 'b -> 'c * 'd) -> 'a * 'b -> 'c * ('a * 'd)

   val pass: 'a -> ('a * 'b -> 'c * ('d * 'e)) -> 'b -> 'c * 'e

   val lift: ('a -> 'b * 'c) -> 'd * 'a -> 'b * ('d * 'c)

   val unlift: (unit * 'a -> 'b * ('c * 'd)) -> 'a -> 'b * 'd

   val trace: ('a list -> 'b * 'c list) -> 'a list -> ('b * 'a list) * 'c list

   type 'a stopper

   val stopper: ('a list -> 'a) -> ('a -> bool) -> 'a stopper

   val is_stopper: 'a stopper -> 'a -> bool

   val finite': 'a stopper -> ('b * 'a list -> 'c * ('d * 'a list))

     -> 'b * 'a list -> 'c * ('d * 'a list)

   val finite: 'a stopper -> ('a list -> 'b * 'a list) -> 'a list -> 'b * 'a list

   val read: 'a stopper -> ('a list -> 'b * 'a list) -> 'a list -> 'b option

   val drain: string -> (string -> 'a -> 'b list * 'a) -> 'b stopper ->

     ('c * 'b list -> 'd * ('e * 'b list)) -> ('c * 'b list) * 'a -> ('d * ('e * 'b list)) * 'a

   type lexicon

   val is_literal: lexicon -> string list -> bool

   val literal: lexicon -> (string * 'a) list -> (string * 'a) list * (string * 'a) list

   val empty_lexicon: lexicon

   val extend_lexicon: string list -> lexicon -> lexicon

   val make_lexicon: string list list -> lexicon

   val dest_lexicon: lexicon -> string list

   val merge_lexicons: lexicon * lexicon -> lexicon

 end;

 structure Scan: SCAN =

 struct

 (** scanners **)

 (* exceptions *)

 type message = unit -> string;

 exception MORE of string option;        (*need more input (prompt)*)

 exception FAIL of message option;       (*try alternatives (reason of failure)*)

 exception ABORT of message;             (*dead end*)

 fun !! err scan xs = scan xs handle FAIL msg => raise ABORT (err (xs, msg));

 fun permissive scan xs = scan xs handle MORE _ => raise FAIL NONE | ABORT _ => raise FAIL NONE;

 fun strict scan xs = scan xs handle MORE _ => raise FAIL NONE;

 fun prompt str scan xs = scan xs handle MORE NONE => raise MORE (SOME str);

 fun error scan xs = scan xs handle ABORT msg => Library.error (msg ());

 fun catch scan xs = scan xs

   handle ABORT msg => raise Fail (msg ())

     | FAIL msg => raise Fail (case msg of NONE => "Syntax error" | SOME m => m ());

 (* scanner combinators *)

 fun (scan >> f) xs = scan xs |>> f;

 fun (scan1 || scan2) xs = scan1 xs handle FAIL _ => scan2 xs;

 fun (scan1 :-- scan2) xs =

   let

     val (x, ys) = scan1 xs;

     val (y, zs) = scan2 x ys;

   in ((x, y), zs) end;

 fun (scan1 -- scan2) = scan1 :-- (fn _ => scan2);

 fun (scan1 :|-- scan2) = scan1 :-- scan2 >> #2;

 fun (scan1 |-- scan2) = scan1 -- scan2 >> #2;

 fun (scan1 --| scan2) = scan1 -- scan2 >> #1;

 fun (scan1 ^^ scan2) = scan1 -- scan2 >> op ^;

 fun (scan1 ::: scan2) = scan1 -- scan2 >> op ::;

 fun (scan1 @@@ scan2) = scan1 -- scan2 >> op @;

 (* generic scanners *)

 fun fail _ = raise FAIL NONE;

 fun fail_with msg_of xs = raise FAIL (SOME (msg_of xs));

 fun succeed y xs = (y, xs);

 fun some _ [] = raise MORE NONE

   | some f (x :: xs) =

       (case f x of SOME y => (y, xs) | _ => raise FAIL NONE);

 fun one _ [] = raise MORE NONE

   | one pred (x :: xs) =

       if pred x then (x, xs) else raise FAIL NONE;

 fun $$ a = one (fn s: string => s = a);

 fun ~$$ a = one (fn s: string => s <> a);

 fun this ys xs =

   let

     fun drop_prefix [] xs = xs

       | drop_prefix (_ :: _) [] = raise MORE NONE

       | drop_prefix (y :: ys) (x :: xs) =

           if (y: string) = x then drop_prefix ys xs else raise FAIL NONE;

   in (ys, drop_prefix ys xs) end;

 fun this_string s = this (raw_explode s) >> K s;  (*primitive string -- no symbols here!*)

 fun many _ [] = raise MORE NONE

   | many pred (lst as x :: xs) =

       if pred x then apfst (cons x) (many pred xs)

       else ([], lst);

 fun many1 pred = one pred ::: many pred;

 fun optional scan def = scan || succeed def;

 fun option scan = (scan >> SOME) || succeed NONE;

 fun repeat scan =

   let

     fun rep ys xs =

       (case (SOME (scan xs) handle FAIL _ => NONE) of

         NONE => (rev ys, xs)

       | SOME (y, xs') => rep (y :: ys) xs');

   in rep [] end;

 fun repeat1 scan = scan ::: repeat scan;

 fun single scan = scan >> (fn x => [x]);

 fun bulk scan = scan -- repeat (permissive scan) >> (op ::);

 fun max leq scan1 scan2 xs =

   (case (option scan1 xs, option scan2 xs) of

     ((NONE, _), (NONE, _)) => raise FAIL NONE           (*looses FAIL msg!*)

   | ((SOME tok1, xs'), (NONE, _)) => (tok1, xs')

   | ((NONE, _), (SOME tok2, xs')) => (tok2, xs')

   | ((SOME tok1, xs1'), (SOME tok2, xs2')) =>

       if leq (tok2, tok1) then (tok1, xs1') else (tok2, xs2'));

 fun ahead scan xs = (fst (scan xs), xs);

 fun unless test scan =

   ahead (option test) :-- (fn NONE => scan | _ => fail) >> #2;

 fun first [] = fail

   | first (scan :: scans) = scan || first scans;

 (* state based scanners *)

 fun state (st, xs) = (st, (st, xs));

 fun depend scan (st, xs) =

   let val ((st', y), xs') = scan st xs

   in (y, (st', xs')) end;

 fun peek scan = depend (fn st => scan st >> pair st);

 fun pass st scan xs =

   let val (y, (_, xs')) = scan (st, xs)

   in (y, xs') end;

 fun lift scan (st, xs) =

   let val (y, xs') = scan xs

   in (y, (st, xs')) end;

 fun unlift scan = pass () scan;

 (* trace input *)

 fun trace scan xs =

   let val (y, xs') = scan xs

   in ((y, take (length xs - length xs') xs), xs') end;

 (* stopper *)

 datatype 'a stopper = Stopper of ('a list -> 'a) * ('a -> bool);

 fun stopper mk_stopper is_stopper = Stopper (mk_stopper, is_stopper);

 fun is_stopper (Stopper (_, is_stopper)) = is_stopper;

 (* finite scans *)

 fun finite' (Stopper (mk_stopper, is_stopper)) scan (state, input) =

   let

     fun lost () = raise ABORT (fn () => "Bad scanner: lost stopper of finite scan!");

     fun stop [] = lost ()

       | stop lst =

           let val (xs, x) = split_last lst

           in if is_stopper x then ((), xs) else lost () end;

   in

     if exists is_stopper input then

       raise ABORT (fn () => "Stopper may not occur in input of finite scan!")

     else (strict scan --| lift stop) (state, input @ [mk_stopper input])

   end;

 fun finite stopper scan = unlift (finite' stopper (lift scan));

 fun read stopper scan xs =

   (case error (finite stopper (option scan)) xs of

     (y as SOME _, []) => y

   | _ => NONE);

 (* infinite scans -- draining state-based source *)

 fun drain def_prompt get stopper scan ((state, xs), src) =

   (scan (state, xs), src) handle MORE prompt =>

     (case get (the_default def_prompt prompt) src of

       ([], _) => (finite' stopper scan (state, xs), src)

     | (xs', src') => drain def_prompt get stopper scan ((state, xs @ xs'), src'));

 (** datatype lexicon -- position tree **)

 datatype lexicon = Lexicon of (bool * lexicon) Symtab.table;

 val empty_lexicon = Lexicon Symtab.empty;

 fun is_literal _ [] = false

   | is_literal (Lexicon tab) (c :: cs) =

       (case Symtab.lookup tab c of

         SOME (tip, lex) => tip andalso null cs orelse is_literal lex cs

       | NONE => false);

 (* scan longest match *)

 fun literal lexicon =

   let

     fun finish (SOME (res, rest)) = (rev res, rest)

       | finish NONE = raise FAIL NONE;

     fun scan _ res (Lexicon tab) [] = if Symtab.is_empty tab then finish res else raise MORE NONE

       | scan path res (Lexicon tab) (c :: cs) =

           (case Symtab.lookup tab (fst c) of

             SOME (tip, lex) =>

               let val path' = c :: path

               in scan path' (if tip then SOME (path', cs) else res) lex cs end

           | NONE => finish res);

   in scan [] NONE lexicon end;

 (* build lexicons *)

 fun extend_lexicon chrs lexicon =

   let

     fun ext [] lex = lex

       | ext (c :: cs) (Lexicon tab) =

           (case Symtab.lookup tab c of

             SOME (tip, lex) => Lexicon (Symtab.update (c, (tip orelse null cs, ext cs lex)) tab)

           | NONE => Lexicon (Symtab.update (c, (null cs, ext cs empty_lexicon)) tab));

   in if is_literal lexicon chrs then lexicon else ext chrs lexicon end;

 fun make_lexicon chrss = fold extend_lexicon chrss empty_lexicon;

 (* merge lexicons *)

 fun dest path (Lexicon tab) = Symtab.fold (fn (d, (tip, lex)) =>

   let

     val path' = d :: path;

     val content = dest path' lex;

   in append (if tip then rev path' :: content else content) end) tab [];

 val dest_lexicon = map implode o dest [];

 fun merge_lexicons (lex1, lex2) = fold extend_lexicon (dest [] lex2) lex1;

 end;

 structure Basic_Scan: BASIC_SCAN = Scan;

 open Basic_Scan;