Annotation of /sml/trunk/src/cm/util/dyn-tstamp.sml

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Revision 302 - (view) (download)

1 :	blume	295	(*
2 :			* "Time" stamps for dynamic envirenments.
3 :			*
4 :			* Copyright (c) 1998 by Lucent, Bell Laboratories
5 :			*
6 :			* author: Matthias Blume (blume@cs.princeton.edu)
7 :			*)
8 :			signature DYNTSTAMP = sig
9 :
10 :			type dts
11 :
12 :			val bogus: dts
13 :			val ancient: dts
14 :
15 :			val reset: unit -> unit
16 :			val new: unit -> unit
17 :
18 :			val current: unit -> dts
19 :			val noshare: string -> dts
20 :
21 :			val outdated: { context: dts, oldresult: dts } -> bool
22 :			val join: dts * dts -> dts
23 :			val can'tShare: dts -> string list option
24 :			end
25 :
26 :			structure DynTStamp :> DYNTSTAMP = struct
27 :
28 :			datatype dts =
29 :			SHARE of int
30 :			| NOSHARE of StringSet.set
31 :
32 :			local
33 :			val era = ref 0
34 :			in
35 :			fun current () = SHARE (!era)
36 :			fun reset () = era := 0
37 :			fun new () = era := (!era) + 1
38 :			end
39 :
40 :			val bogus = SHARE 0
41 :			val ancient = SHARE (~1)
42 :
43 :			fun noshare s = NOSHARE (StringSet.singleton s)
44 :
45 :	blume	302	(* The only time we can encounter an old result of NOSHARE is
46 :			* during the same run of "make". In this case, the old value
47 :			* certainly cannot be outdated. *)
48 :	blume	295	fun outdated { context = SHARE c, oldresult = SHARE r } = c > r
49 :	blume	302	| outdated { oldresult = NOSHARE _, ... } = false
50 :	blume	295	| outdated _ = true
51 :
52 :			fun join (SHARE x, SHARE y) = SHARE (if x > y then x else y)
53 :			| join (x as NOSHARE _, SHARE _) = x
54 :			| join (SHARE _, x as NOSHARE _) = x
55 :			| join (NOSHARE x, NOSHARE y) = NOSHARE (StringSet.union (x, y))
56 :
57 :			fun can'tShare (NOSHARE s) = SOME (StringSet.listItems s)
58 :			| can'tShare _ = NONE
59 :			end

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