begin work on between library

2019-02-23 19:59:13 -07:00
parent 20b66e283f
commit 67ae47a01a
8 changed files with 83 additions and 49 deletions
--- a/src/prolog/examples/minatotask.pl
+++ b/src/prolog/examples/minatotask.pl
@@ -0,0 +1,112 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   SICStus implementation of the Minato task.
+   Written Sept. 2017 by Markus Triska (triska@metalevel.at)
+   Public domain code.
+
+   For more information, please see:
+
+   https://www.metalevel.at/prolog/attributedvariables
+   ===================================================
+
+   A ZDD node is either:
+
+       -) a *leaf* of the form b(true) or b(false)
+       -) an *inner node* of the form ( Var -> Then ; Else ).
+
+   In ZDDs, variables that are *not* encountered on a path to TRUE
+   must be 0.
+
+   This module exports a single predicate:
+
+   * variables_set_zdd(Vs, ZDD)
+
+   It associates each variable in Vs with the given ZDD. For each
+   variable, the ZDD is stored as an attribute zdd_vs(ZDD, Vs).  This
+   lets us reason about all variables that originally occurred.
+
+   The internal unification hooks must be implemented so that only
+   admissible assignments of truth variables to variables succeed.
+
+   In particular, the Minato task:
+
+   ?- ZDD = ( X -> b(true) ; ( Y -> b(true) ; b(false) ) ),
+      Vs = [X,Y],
+      variables_set_zdd(Vs, ZDD),
+      Vs = [1,1].
+
+           no
+
+   Other examples:
+
+   ?- ZDD = ( X -> b(true) ; ( Y -> b(true) ; b(false) ) ),
+      Vs = [X,Y],
+      variables_set_zdd(Vs, ZDD),
+      X = 1.
+
+           X = 1,
+           Y = 0,
+           Vs = [1,0] ? ;
+
+
+   ?- ZDD = ( X -> b(true) ; ( Y -> b(true) ; b(false) ) ),
+      Vs = [X,Y],
+      variables_set_zdd(Vs, ZDD),
+      X = 0.
+
+           X = 0,
+           Vs = [0,Y] ? ;
+
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(zdd, [variables_set_zdd/2]).
+
+:- use_module(library(atts)).
+:- use_module(library(dcgs)).
+:- use_module(library(lists)).
+
+:- attribute zdd_vs/2.
+
+variables_set_zdd(Vs, ZDD) :-
+        maplist(set_zdd(ZDD, Vs), Vs).
+
+set_zdd(ZDD, Vs, V) :-
+        put_atts(V, +zdd_vs(ZDD, Vs)).
+
+
+verify_attributes(Var, Value, Goals) :-
+        (   get_atts(Var, +zdd_vs(ZDD0,Vs)) ->
+            (   integer(Value) ->
+                zdd_restriction(ZDD0, Var, Value, ZDD)
+            ;   throw(aliasing_not_implemented)
+            ),
+            phrase(remaining_vars_0(ZDD, Var, Vs), Goals)
+        ;   Goals = []
+        ).
+
+remaining_vars_0(b(true), Var, Vs) --> all_others_0(Vs, Var).
+remaining_vars_0((_;_), _, _) --> [].
+
+all_others_0([], _) --> [].
+all_others_0([V|Vs], Var) -->
+        (   { var(V), V \== Var } -> [V=0]
+        ;   []
+        ),
+        all_others_0(Vs, Var).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Compute the *restriction* of the ZDD.
+   This means that Var has been instantiated to Value.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+zdd_restriction(b(T), _, _, b(T)).
+zdd_restriction(( Var0 -> Then0 ; Else0), Var, Value, ZDD) :-
+        (   Var0 == Var ->
+            (   Value =:= 0 -> ZDD = Else0
+            ;   Value =:= 1 -> ZDD = Then0
+            ;   throw(no_boolean)
+            )
+        ;   zdd_restriction(Then0, Var, Value, Then),
+            zdd_restriction(Else0, Var, Value, Else),
+            ZDD = ( Var0 -> Then ; Else )
+        ).