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(* Title: Pure/General/lazy_scan.ML
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ID: $Id$
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Author: Sebastian Skalberg, TU Muenchen
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Scanner combinators for lazy sequences.
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*)
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signature LAZY_SCAN =
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sig
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exception SyntaxError
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type ('a,'b) scanner = 'a LazySeq.seq -> 'b * 'a LazySeq.seq
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val :-- : ('a,'b) scanner * ('b -> ('a,'c) scanner)
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-> ('a,'b*'c) scanner
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val -- : ('a,'b) scanner * ('a,'c) scanner -> ('a,'b*'c) scanner
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val >> : ('a,'b) scanner * ('b -> 'c) -> ('a,'c) scanner
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val --| : ('a,'b) scanner * ('a,'c) scanner -> ('a,'b) scanner
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val |-- : ('a,'b) scanner * ('a,'c) scanner -> ('a,'c) scanner
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val ^^ : ('a,string) scanner * ('a,string) scanner
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-> ('a,string) scanner
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val || : ('a,'b) scanner * ('a,'b) scanner -> ('a,'b) scanner
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val one : ('a -> bool) -> ('a,'a) scanner
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val succeed : 'b -> ('a,'b) scanner
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val any : ('a -> bool) -> ('a,'a list) scanner
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val any1 : ('a -> bool) -> ('a,'a list) scanner
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val optional : ('a,'b) scanner -> 'b -> ('a,'b) scanner
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val option : ('a,'b) scanner -> ('a,'b option) scanner
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val repeat : ('a,'b) scanner -> ('a,'b list) scanner
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val repeat1 : ('a,'b) scanner -> ('a,'b list) scanner
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val ahead : ('a,'b) scanner -> ('a,'b) scanner
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val unless : ('a LazySeq.seq -> bool) -> ('a,'b) scanner -> ('a,'b) scanner
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val $$ : ''a -> (''a,''a) scanner
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val !! : ('a LazySeq.seq -> string) -> ('a,'b) scanner -> ('a,'b) scanner
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val scan_full: ('a,'b) scanner -> 'a LazySeq.seq -> 'b LazySeq.seq
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end
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structure LazyScan :> LAZY_SCAN =
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struct
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infix 7 |-- --|
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infix 5 :-- -- ^^
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infix 3 >>
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infix 0 ||
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exception SyntaxError
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exception Fail of string
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type ('a,'b) scanner = 'a LazySeq.seq -> 'b * 'a LazySeq.seq
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fun (sc1 :-- sc2) toks =
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let
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val (x,toks2) = sc1 toks
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val (y,toks3) = sc2 x toks2
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in
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((x,y),toks3)
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end
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fun (sc1 -- sc2) toks =
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let
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val (x,toks2) = sc1 toks
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val (y,toks3) = sc2 toks2
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in
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((x,y),toks3)
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end
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fun (sc >> f) toks =
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let
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val (x,toks2) = sc toks
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in
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(f x,toks2)
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end
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fun (sc1 --| sc2) toks =
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let
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val (x,toks2) = sc1 toks
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val (_,toks3) = sc2 toks2
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in
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(x,toks3)
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end
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fun (sc1 |-- sc2) toks =
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let
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val (_,toks2) = sc1 toks
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in
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sc2 toks2
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end
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fun (sc1 ^^ sc2) toks =
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let
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val (x,toks2) = sc1 toks
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val (y,toks3) = sc2 toks2
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in
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(x^y,toks3)
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end
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fun (sc1 || sc2) toks =
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(sc1 toks)
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handle SyntaxError => sc2 toks
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fun one p toks =
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case LazySeq.getItem toks of
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NONE => raise SyntaxError
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| SOME(t,toks) => if p t
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then (t,toks)
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else raise SyntaxError
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fun succeed e toks = (e,toks)
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fun any p toks =
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case LazySeq.getItem toks of
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NONE => ([],toks)
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| SOME(x,toks2) => if p x
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then
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let
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val (xs,toks3) = any p toks2
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in
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(x::xs,toks3)
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end
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else ([],toks)
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fun any1 p toks =
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let
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val (x,toks2) = one p toks
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val (xs,toks3) = any p toks2
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in
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(x::xs,toks3)
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end
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fun optional sc def = sc || succeed def
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fun option sc = (sc >> SOME) || succeed NONE
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(*
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fun repeat sc =
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let
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fun R toks =
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let
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val (x,toks2) = sc toks
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val (xs,toks3) = R toks2
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in
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(x::xs,toks3)
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end
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handle SyntaxError => ([],toks)
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in
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R
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end
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*)
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(* A tail-recursive version of repeat. It is (ever so) slightly slower
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* than the above, non-tail-recursive version (due to the garbage generation
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* associated with the reversal of the list). However, this version will be
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* able to process input where the former version must give up (due to stack
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* overflow). The slowdown seems to be around the one percent mark.
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*)
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fun repeat sc =
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let
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fun R xs toks =
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case SOME (sc toks) handle SyntaxError => NONE of
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SOME (x,toks2) => R (x::xs) toks2
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| NONE => (List.rev xs,toks)
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in
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R []
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end
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fun repeat1 sc toks =
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let
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val (x,toks2) = sc toks
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val (xs,toks3) = repeat sc toks2
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in
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(x::xs,toks3)
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end
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fun ahead (sc:'a->'b*'a) toks = (#1 (sc toks),toks)
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fun unless test sc toks =
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let
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val test_failed = (test toks;false) handle SyntaxError => true
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in
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if test_failed
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then sc toks
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else raise SyntaxError
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end
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fun $$ arg = one (fn x => x = arg)
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fun !! f sc toks = (sc toks
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handle SyntaxError => raise Fail (f toks))
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fun scan_full sc toks =
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let
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fun F toks =
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if LazySeq.null toks
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then NONE
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else
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let
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val (x,toks') = sc toks
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in
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SOME(x,LazySeq.make (fn () => F toks'))
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end
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in
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LazySeq.make (fn () => F toks)
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end
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end
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