src/Pure/net.ML
author wenzelm
Sat May 15 23:23:45 2010 +0200 (2010-05-15)
changeset 36951 985c197f2fe9
parent 33371 d74dc1b54930
child 37523 40c352510065
permissions -rw-r--r--
renamed structure ValueParse to Parse_Value;
eliminated old-style structure alias V;
wenzelm@12319
     1
(*  Title:      Pure/net.ML
wenzelm@12319
     2
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
clasohm@0
     3
    Copyright   1993  University of Cambridge
clasohm@0
     4
clasohm@0
     5
Discrimination nets: a data structure for indexing items
clasohm@0
     6
wenzelm@12319
     7
From the book
wenzelm@12319
     8
    E. Charniak, C. K. Riesbeck, D. V. McDermott.
clasohm@0
     9
    Artificial Intelligence Programming.
clasohm@0
    10
    (Lawrence Erlbaum Associates, 1980).  [Chapter 14]
nipkow@225
    11
wenzelm@12319
    12
match_term no longer treats abstractions as wildcards; instead they match
nipkow@228
    13
only wildcards in patterns.  Requires operands to be beta-eta-normal.
clasohm@0
    14
*)
clasohm@0
    15
wenzelm@12319
    16
signature NET =
wenzelm@16808
    17
sig
clasohm@0
    18
  type key
wenzelm@16808
    19
  val key_of_term: term -> key list
clasohm@0
    20
  type 'a net
clasohm@0
    21
  val empty: 'a net
wenzelm@16808
    22
  exception INSERT
wenzelm@16808
    23
  val insert: ('a * 'a -> bool) -> key list * 'a -> 'a net -> 'a net
wenzelm@16808
    24
  val insert_term: ('a * 'a -> bool) -> term * 'a -> 'a net -> 'a net
wenzelm@33371
    25
  val insert_safe: ('a * 'a -> bool) -> key list * 'a -> 'a net -> 'a net
wenzelm@33371
    26
  val insert_term_safe: ('a * 'a -> bool) -> term * 'a -> 'a net -> 'a net
wenzelm@16808
    27
  exception DELETE
wenzelm@16808
    28
  val delete: ('b * 'a -> bool) -> key list * 'b -> 'a net -> 'a net
wenzelm@16808
    29
  val delete_term: ('b * 'a -> bool) -> term * 'b -> 'a net -> 'a net
wenzelm@33371
    30
  val delete_safe: ('b * 'a -> bool) -> key list * 'b -> 'a net -> 'a net
wenzelm@33371
    31
  val delete_term_safe: ('b * 'a -> bool) -> term * 'b -> 'a net -> 'a net
wenzelm@16808
    32
  val lookup: 'a net -> key list -> 'a list
clasohm@0
    33
  val match_term: 'a net -> term -> 'a list
clasohm@0
    34
  val unify_term: 'a net -> term -> 'a list
wenzelm@16808
    35
  val entries: 'a net -> 'a list
wenzelm@16808
    36
  val subtract: ('b * 'a -> bool) -> 'a net -> 'b net -> 'b list
wenzelm@16808
    37
  val merge: ('a * 'a -> bool) -> 'a net * 'a net -> 'a net
wenzelm@20011
    38
  val content: 'a net -> 'a list
wenzelm@16808
    39
end;
clasohm@0
    40
wenzelm@16808
    41
structure Net: NET =
clasohm@0
    42
struct
clasohm@0
    43
clasohm@0
    44
datatype key = CombK | VarK | AtomK of string;
clasohm@0
    45
nipkow@228
    46
(*Keys are preorder lists of symbols -- Combinations, Vars, Atoms.
nipkow@225
    47
  Any term whose head is a Var is regarded entirely as a Var.
nipkow@228
    48
  Abstractions are also regarded as Vars;  this covers eta-conversion
nipkow@228
    49
    and "near" eta-conversions such as %x.?P(?f(x)).
clasohm@0
    50
*)
wenzelm@12319
    51
fun add_key_of_terms (t, cs) =
clasohm@0
    52
  let fun rands (f$t, cs) = CombK :: rands (f, add_key_of_terms(t, cs))
wenzelm@12319
    53
        | rands (Const(c,_), cs) = AtomK c :: cs
wenzelm@12319
    54
        | rands (Free(c,_),  cs) = AtomK c :: cs
wenzelm@20080
    55
        | rands (Bound i,  cs)   = AtomK (Name.bound i) :: cs
clasohm@0
    56
  in case (head_of t) of
nipkow@225
    57
      Var _ => VarK :: cs
nipkow@228
    58
    | Abs _ => VarK :: cs
nipkow@225
    59
    | _     => rands(t,cs)
clasohm@0
    60
  end;
clasohm@0
    61
nipkow@225
    62
(*convert a term to a list of keys*)
clasohm@0
    63
fun key_of_term t = add_key_of_terms (t, []);
clasohm@0
    64
clasohm@0
    65
clasohm@0
    66
(*Trees indexed by key lists: each arc is labelled by a key.
clasohm@0
    67
  Each node contains a list of items, and arcs to children.
clasohm@0
    68
  The empty key addresses the entire net.
clasohm@0
    69
  Lookup functions preserve order in items stored at same level.
clasohm@0
    70
*)
clasohm@0
    71
datatype 'a net = Leaf of 'a list
wenzelm@12319
    72
                | Net of {comb: 'a net,
wenzelm@12319
    73
                          var: 'a net,
wenzelm@16708
    74
                          atoms: 'a net Symtab.table};
clasohm@0
    75
clasohm@0
    76
val empty = Leaf[];
wenzelm@16708
    77
fun is_empty (Leaf []) = true | is_empty _ = false;
wenzelm@16708
    78
val emptynet = Net{comb=empty, var=empty, atoms=Symtab.empty};
clasohm@0
    79
clasohm@0
    80
clasohm@0
    81
(*** Insertion into a discrimination net ***)
clasohm@0
    82
wenzelm@12319
    83
exception INSERT;       (*duplicate item in the net*)
clasohm@0
    84
clasohm@0
    85
clasohm@0
    86
(*Adds item x to the list at the node addressed by the keys.
clasohm@0
    87
  Creates node if not already present.
wenzelm@12319
    88
  eq is the equality test for items.
clasohm@0
    89
  The empty list of keys generates a Leaf node, others a Net node.
clasohm@0
    90
*)
wenzelm@16808
    91
fun insert eq (keys,x) net =
wenzelm@12319
    92
  let fun ins1 ([], Leaf xs) =
wenzelm@16686
    93
            if member eq xs x then  raise INSERT  else Leaf(x::xs)
clasohm@0
    94
        | ins1 (keys, Leaf[]) = ins1 (keys, emptynet)   (*expand empty...*)
wenzelm@16708
    95
        | ins1 (CombK :: keys, Net{comb,var,atoms}) =
wenzelm@16708
    96
            Net{comb=ins1(keys,comb), var=var, atoms=atoms}
wenzelm@16708
    97
        | ins1 (VarK :: keys, Net{comb,var,atoms}) =
wenzelm@16708
    98
            Net{comb=comb, var=ins1(keys,var), atoms=atoms}
wenzelm@16708
    99
        | ins1 (AtomK a :: keys, Net{comb,var,atoms}) =
wenzelm@16708
   100
            let
wenzelm@18939
   101
              val net' = the_default empty (Symtab.lookup atoms a);
wenzelm@17412
   102
              val atoms' = Symtab.update (a, ins1 (keys, net')) atoms;
wenzelm@16708
   103
            in  Net{comb=comb, var=var, atoms=atoms'}  end
clasohm@0
   104
  in  ins1 (keys,net)  end;
clasohm@0
   105
wenzelm@33371
   106
fun insert_term eq (t, x) = insert eq (key_of_term t, x);
wenzelm@33371
   107
wenzelm@16808
   108
fun insert_safe eq entry net = insert eq entry net handle INSERT => net;
wenzelm@33371
   109
fun insert_term_safe eq entry net = insert_term eq entry net handle INSERT => net;
wenzelm@16808
   110
clasohm@0
   111
clasohm@0
   112
(*** Deletion from a discrimination net ***)
clasohm@0
   113
wenzelm@12319
   114
exception DELETE;       (*missing item in the net*)
clasohm@0
   115
clasohm@0
   116
(*Create a new Net node if it would be nonempty*)
wenzelm@16708
   117
fun newnet (args as {comb,var,atoms}) =
wenzelm@16708
   118
  if is_empty comb andalso is_empty var andalso Symtab.is_empty atoms
wenzelm@16708
   119
  then empty else Net args;
clasohm@0
   120
clasohm@0
   121
(*Deletes item x from the list at the node addressed by the keys.
clasohm@0
   122
  Raises DELETE if absent.  Collapses the net if possible.
clasohm@0
   123
  eq is the equality test for items. *)
wenzelm@16808
   124
fun delete eq (keys, x) net =
clasohm@0
   125
  let fun del1 ([], Leaf xs) =
wenzelm@16686
   126
            if member eq xs x then Leaf (remove eq x xs)
clasohm@0
   127
            else raise DELETE
wenzelm@12319
   128
        | del1 (keys, Leaf[]) = raise DELETE
wenzelm@16708
   129
        | del1 (CombK :: keys, Net{comb,var,atoms}) =
wenzelm@16708
   130
            newnet{comb=del1(keys,comb), var=var, atoms=atoms}
wenzelm@16708
   131
        | del1 (VarK :: keys, Net{comb,var,atoms}) =
wenzelm@16708
   132
            newnet{comb=comb, var=del1(keys,var), atoms=atoms}
wenzelm@16708
   133
        | del1 (AtomK a :: keys, Net{comb,var,atoms}) =
wenzelm@16708
   134
            let val atoms' =
wenzelm@17412
   135
              (case Symtab.lookup atoms a of
wenzelm@16708
   136
                NONE => raise DELETE
wenzelm@16708
   137
              | SOME net' =>
wenzelm@16708
   138
                  (case del1 (keys, net') of
wenzelm@16708
   139
                    Leaf [] => Symtab.delete a atoms
wenzelm@17412
   140
                  | net'' => Symtab.update (a, net'') atoms))
wenzelm@16708
   141
            in  newnet{comb=comb, var=var, atoms=atoms'}  end
clasohm@0
   142
  in  del1 (keys,net)  end;
clasohm@0
   143
wenzelm@16808
   144
fun delete_term eq (t, x) = delete eq (key_of_term t, x);
clasohm@0
   145
wenzelm@33371
   146
fun delete_safe eq entry net = delete eq entry net handle DELETE => net;
wenzelm@33371
   147
fun delete_term_safe eq entry net = delete_term eq entry net handle DELETE => net;
wenzelm@33371
   148
wenzelm@16677
   149
clasohm@0
   150
(*** Retrieval functions for discrimination nets ***)
clasohm@0
   151
wenzelm@16708
   152
exception ABSENT;
clasohm@0
   153
wenzelm@16708
   154
fun the_atom atoms a =
wenzelm@17412
   155
  (case Symtab.lookup atoms a of
wenzelm@16708
   156
    NONE => raise ABSENT
wenzelm@16708
   157
  | SOME net => net);
clasohm@0
   158
clasohm@0
   159
(*Return the list of items at the given node, [] if no such node*)
wenzelm@16808
   160
fun lookup (Leaf xs) [] = xs
wenzelm@16808
   161
  | lookup (Leaf _) (_ :: _) = []  (*non-empty keys and empty net*)
wenzelm@16808
   162
  | lookup (Net {comb, var, atoms}) (CombK :: keys) = lookup comb keys
wenzelm@16808
   163
  | lookup (Net {comb, var, atoms}) (VarK :: keys) = lookup var keys
wenzelm@16808
   164
  | lookup (Net {comb, var, atoms}) (AtomK a :: keys) =
wenzelm@16808
   165
      lookup (the_atom atoms a) keys handle ABSENT => [];
clasohm@0
   166
clasohm@0
   167
clasohm@0
   168
(*Skipping a term in a net.  Recursively skip 2 levels if a combination*)
wenzelm@23178
   169
fun net_skip (Leaf _) nets = nets
wenzelm@23178
   170
  | net_skip (Net{comb,var,atoms}) nets =
wenzelm@23178
   171
      fold_rev net_skip (net_skip comb []) (Symtab.fold (cons o #2) atoms (var::nets));
clasohm@0
   172
wenzelm@16808
   173
wenzelm@16808
   174
(** Matching and Unification **)
clasohm@0
   175
clasohm@0
   176
(*conses the linked net, if present, to nets*)
wenzelm@16708
   177
fun look1 (atoms, a) nets =
wenzelm@16708
   178
  the_atom atoms a :: nets handle ABSENT => nets;
clasohm@0
   179
wenzelm@12319
   180
(*Return the nodes accessible from the term (cons them before nets)
clasohm@0
   181
  "unif" signifies retrieval for unification rather than matching.
clasohm@0
   182
  Var in net matches any term.
wenzelm@12319
   183
  Abs or Var in object: if "unif", regarded as wildcard,
nipkow@225
   184
                                   else matches only a variable in net.
nipkow@225
   185
*)
wenzelm@23178
   186
fun matching unif t net nets =
clasohm@0
   187
  let fun rands _ (Leaf _, nets) = nets
wenzelm@16708
   188
        | rands t (Net{comb,atoms,...}, nets) =
wenzelm@12319
   189
            case t of
wenzelm@23178
   190
                f$t => fold_rev (matching unif t) (rands f (comb,[])) nets
wenzelm@16708
   191
              | Const(c,_) => look1 (atoms, c) nets
wenzelm@16708
   192
              | Free(c,_)  => look1 (atoms, c) nets
wenzelm@20080
   193
              | Bound i    => look1 (atoms, Name.bound i) nets
wenzelm@12319
   194
              | _          => nets
wenzelm@12319
   195
  in
clasohm@0
   196
     case net of
wenzelm@12319
   197
         Leaf _ => nets
clasohm@0
   198
       | Net{var,...} =>
wenzelm@12319
   199
             case head_of t of
wenzelm@23178
   200
                 Var _ => if unif then net_skip net nets
wenzelm@12319
   201
                          else var::nets           (*only matches Var in net*)
paulson@2836
   202
  (*If "unif" then a var instantiation in the abstraction could allow
paulson@2836
   203
    an eta-reduction, so regard the abstraction as a wildcard.*)
wenzelm@23178
   204
               | Abs _ => if unif then net_skip net nets
wenzelm@12319
   205
                          else var::nets           (*only a Var can match*)
wenzelm@12319
   206
               | _ => rands t (net, var::nets)  (*var could match also*)
clasohm@0
   207
  end;
clasohm@0
   208
wenzelm@19482
   209
fun extract_leaves l = maps (fn Leaf xs => xs) l;
clasohm@0
   210
nipkow@225
   211
(*return items whose key could match t, WHICH MUST BE BETA-ETA NORMAL*)
wenzelm@12319
   212
fun match_term net t =
wenzelm@23178
   213
    extract_leaves (matching false t net []);
clasohm@0
   214
clasohm@0
   215
(*return items whose key could unify with t*)
wenzelm@12319
   216
fun unify_term net t =
wenzelm@23178
   217
    extract_leaves (matching true t net []);
clasohm@0
   218
wenzelm@3548
   219
wenzelm@16808
   220
(** operations on nets **)
wenzelm@16808
   221
wenzelm@16808
   222
(*subtraction: collect entries of second net that are NOT present in first net*)
wenzelm@16808
   223
fun subtract eq net1 net2 =
wenzelm@16808
   224
  let
wenzelm@16808
   225
    fun subtr (Net _) (Leaf ys) = append ys
wenzelm@16808
   226
      | subtr (Leaf xs) (Leaf ys) =
wenzelm@16808
   227
          fold_rev (fn y => if member eq xs y then I else cons y) ys
wenzelm@16808
   228
      | subtr (Leaf _) (net as Net _) = subtr emptynet net
wenzelm@16808
   229
      | subtr (Net {comb = comb1, var = var1, atoms = atoms1})
wenzelm@16808
   230
            (Net {comb = comb2, var = var2, atoms = atoms2}) =
wenzelm@16842
   231
          subtr comb1 comb2
wenzelm@16842
   232
          #> subtr var1 var2
wenzelm@16842
   233
          #> Symtab.fold (fn (a, net) =>
wenzelm@18939
   234
            subtr (the_default emptynet (Symtab.lookup atoms1 a)) net) atoms2
wenzelm@16808
   235
  in subtr net1 net2 [] end;
wenzelm@16808
   236
wenzelm@16808
   237
fun entries net = subtract (K false) empty net;
wenzelm@16808
   238
wenzelm@16808
   239
wenzelm@16808
   240
(* merge *)
wenzelm@3548
   241
wenzelm@3548
   242
fun cons_fst x (xs, y) = (x :: xs, y);
wenzelm@3548
   243
wenzelm@3548
   244
fun dest (Leaf xs) = map (pair []) xs
wenzelm@16708
   245
  | dest (Net {comb, var, atoms}) =
wenzelm@3560
   246
      map (cons_fst CombK) (dest comb) @
wenzelm@3560
   247
      map (cons_fst VarK) (dest var) @
wenzelm@19482
   248
      maps (fn (a, net) => map (cons_fst (AtomK a)) (dest net)) (Symtab.dest atoms);
wenzelm@3548
   249
wenzelm@16808
   250
fun merge eq (net1, net2) = fold (insert_safe eq) (dest net2) net1;
wenzelm@3548
   251
wenzelm@20011
   252
fun content net = map #2 (dest net);
wenzelm@20011
   253
clasohm@0
   254
end;