src/Pure/context.ML
author wenzelm
Tue, 09 Mar 1999 12:05:07 +0100
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(*  Title:      Pure/context.ML
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    ID:         $Id$
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    Author:     Markus Wenzel, TU Muenchen
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Global theory context.
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*)
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signature BASIC_CONTEXT =
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sig
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  val context: theory -> unit
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  val the_context: unit -> theory
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end;
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signature CONTEXT =
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sig
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  include BASIC_CONTEXT
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  val get_context: unit -> theory option
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  val set_context: theory option -> unit
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  val reset_context: unit -> unit
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  val setmp: theory option -> ('a -> 'b) -> 'a -> 'b
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  val pass: theory option -> ('a -> 'b) -> 'a -> 'b * theory option
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  val pass_theory: theory -> ('a -> 'b) -> 'a -> 'b * theory
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  val save: ('a -> 'b) -> 'a -> 'b
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  val >> : (theory -> theory) -> unit
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end;
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structure Context: CONTEXT =
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struct
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(* theory context *)
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local
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  val current_theory = ref (None: theory option);
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in
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  fun get_context () = ! current_theory;
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  fun set_context opt_thy = current_theory := opt_thy;
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  fun setmp opt_thy f x = Library.setmp current_theory opt_thy f x;
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end;
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fun the_context () =
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  (case get_context () of
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    Some thy => thy
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  | _ => error "Unknown theory context");
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fun context thy = set_context (Some thy);
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fun reset_context () = set_context None;
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fun pass opt_thy f x =
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  setmp opt_thy (fn x => let val y = f x in (y, get_context ()) end) x;
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fun pass_theory thy f x =
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  (case pass (Some thy) f x of
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    (y, Some thy') => (y, thy')
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  | (_, None) => error "Missing ML theory context");
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fun save f x = setmp (get_context ()) f x;
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(* map context *)
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nonfix >>;
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fun >> f = set_context (Some (f (the_context ())));
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end;
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structure BasicContext: BASIC_CONTEXT = Context;
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open BasicContext;