src/Pure/Concurrent/par_list.ML
 author haftmann Thu Oct 22 13:48:06 2009 +0200 (2009-10-22) changeset 33063 4d462963a7db parent 32614 fef7022dc5ab child 35393 2f83aa48d696 permissions -rw-r--r--
map_range (and map_index) combinator
```     1 (*  Title:      Pure/Concurrent/par_list.ML
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```     2     Author:     Makarius
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```     3
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```     4 Parallel list combinators.
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```     5
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```     6 Notes:
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```     7
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```     8   * These combinators only make sense if the operator (function or
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```     9     predicate) applied to the list of operands takes considerable
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```    10     time.  The overhead of scheduling is significantly higher than
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```    11     just traversing the list of operands sequentially.
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```    12
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```    13   * The order of operator application is non-deterministic.  Watch out
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```    14     for operators that have side-effects or raise exceptions!
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```    15 *)
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```    16
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```    17 signature PAR_LIST =
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```    18 sig
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```    19   val map: ('a -> 'b) -> 'a list -> 'b list
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```    20   val get_some: ('a -> 'b option) -> 'a list -> 'b option
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```    21   val find_some: ('a -> bool) -> 'a list -> 'a option
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```    22   val exists: ('a -> bool) -> 'a list -> bool
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```    23   val forall: ('a -> bool) -> 'a list -> bool
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```    24 end;
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```    25
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```    26 structure Par_List: PAR_LIST =
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```    27 struct
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```    28
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```    29 fun raw_map f xs =
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```    30   if Multithreading.enabled () then
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```    31     let val group = Task_Queue.new_group (Future.worker_group ())
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```    32     in Future.join_results (map (fn x => Future.fork_group group (fn () => f x)) xs) end
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```    33   else map (Exn.capture f) xs;
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```    34
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```    35 fun map f xs = Exn.release_first (raw_map f xs);
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```    36
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```    37 fun get_some f xs =
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```    38   let
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```    39     exception FOUND of 'b option;
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```    40     fun found (Exn.Exn (FOUND some)) = some
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```    41       | found _ = NONE;
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```    42     val results = raw_map (fn x => (case f x of NONE => () | some => raise FOUND some)) xs;
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```    43   in
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```    44     (case get_first found results of
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```    45       SOME y => SOME y
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```    46     | NONE => (Exn.release_first results; NONE))
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```    47   end;
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```    48
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```    49 fun find_some P = get_some (fn x => if P x then SOME x else NONE);
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```    50
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```    51 fun exists P = is_some o get_some (fn x => if P x then SOME () else NONE);
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```    52 fun forall P = not o exists (not o P);
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```    53
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```    54 end;
```