src/Pure/General/alist.ML
author haftmann
Sun, 28 Aug 2005 09:02:42 +0200
changeset 17152 a696a3d30b97
child 17191 ae9901f856aa
permissions -rw-r--r--
added alist module
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(*  Title:      Pure/General/alist.ML
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    ID:         $Id$
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    Author:     Florian Haftmann, TU Muenchen
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Association lists -- lists of (key, value) pairs with unique keys.
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A light-weight representation of finite mappings;
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see also Pure/General/table.ML for a more scalable implementation.
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*)
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signature ALIST =
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sig
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  val lookup: ('a * 'b -> bool) -> ('b * 'c) list -> 'a -> 'c option
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  val defined: ('a * 'b -> bool) -> ('b * 'c) list -> 'a -> bool
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  val update: ('a * 'a -> bool) -> ('a * 'b)
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    -> ('a * 'b) list -> ('a * 'b) list
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  val default: ('a * 'a -> bool) -> ('a * 'b)
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    -> ('a * 'b) list -> ('a * 'b) list
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  val delete: ('a * 'b -> bool) -> 'a
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    -> ('b * 'c) list -> ('b * 'c) list
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  val map_entry: ('a * 'b -> bool) -> 'a -> ('c -> 'c)
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    -> ('b * 'c) list -> ('b * 'c) list
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end;
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structure AList: ALIST =
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struct
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fun lookup _ [] _ = NONE
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  | lookup eq ((key, value)::xs) key' =
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      if eq (key', key) then SOME value
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      else lookup eq xs key';
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fun defined _ [] _ = false
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  | defined eq ((key, value)::xs) key' =
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      eq (key', key) orelse defined eq xs key';
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fun update eq (key, value) xs =
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  let
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    fun upd ((x as (key', _))::xs) =
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      if eq (key, key')
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      then (key, value)::xs
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      else x :: upd xs
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  in if defined eq xs key then upd xs else (key, value)::xs end;
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fun default eq (key, value) xs =
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  if defined eq xs key then xs else (key, value)::xs;
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fun map_entry eq _ _ [] = []
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  | map_entry eq key' f ((x as (key, value))::xs) =
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      if eq (key', key) then ((key, f value)::xs)
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      else x :: map_entry eq key' f xs;
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fun delete eq key xs =
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  let
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    fun del ((x as (key', _))::xs) =
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      if eq (key, key') then xs
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      else x :: del xs;
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  in if defined eq xs key then del xs else xs end;
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end;