-- Copyright (c) 1991-2002, The Numerical ALgorithms Group Ltd.
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-- Copyright (C) 2007-2011, Gabriel Dos Reis.
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import vmlisp
namespace BOOT
module astr where
  ncTag: %Thing -> %Symbol
  ncAlist: %Thing -> %List %Thing
  ncEltQ: (%List %Thing,%Thing) -> %Thing
  ncPutQ: (%List %Thing,%Thing,%Thing) -> %Thing

--% Attributed Structures (astr)
-- For objects which are pairs where the first field is either just a tag
-- (an identifier) or a pair which is the tag and an association list.
 
-- Pick off the tag
ncTag x ==
   x isnt [.,:.] => ncBug('S2CB0031,[])
   x := first x
   ident? x => x
   x isnt [.,:.] => ncBug('S2CB0031,[])
   first x
 
-- Pick off the property list
ncAlist x ==
   x isnt [.,:.] => ncBug('S2CB0031,[])
   x := first x
   ident? x => nil
   x isnt [.,:.] => ncBug('S2CB0031,[])
   rest x

 --- Get the entry for key k on x's association list
ncEltQ(x,k) ==
   r := objectAssoc(k,ncAlist x) => rest r
   ncBug ('S2CB0007,[k])
 
-- Put (k . v) on the association list of x and return v
-- case1: ncPutQ(x,k,v) where k is a key (an identifier), v a value
--        put the pair (k . v) on the association list of x and return v
-- case2: ncPutQ(x,k,v) where k is a list of keys, v a list of values
--        equivalent to [ncPutQ(x,key,val) for key in k for val in v]
ncPutQ(x,k,v) ==
   LISTP k =>
      for key in k for val in v repeat ncPutQ(x,key,val)
      v
   r := objectAssoc(k,ncAlist x)
   if null r then
      r := [[k,:v], :ncAlist x]
      x.first := [ncTag x,:r]
   else
      r.rest := v
   v