Changeset 4477 for trunk/examples

Timestamp:

10/02/08 08:42:54 (3 months ago)

Author:

pmoura

Message:

Improved "metainterpreters" example.

Location:

trunk/examples/metainterpreters

Files:

• metainterpreters.lgt (modified) (6 diffs)
• NOTES.txt (modified) (1 diff)
• rules.lgt (modified) (2 diffs)

trunk/examples/metainterpreters/metainterpreters.lgt

@@ -3 +3 @@
 
     :- info([
-        version is 1.0,
-        date is 2004/5/2,
+        version is 1.1,
+        date is 2008/10/2,
         author is 'Paulo Moura',
         comment is 'Simple meta-interpreter for pure Prolog with only conjunctions as clause bodies.']).
@@ -21 +21 @@
         solve(B).
     solve(A) :-
-        ::clause(A, B),
+        clause(A, B),   % retrieves clauses in "this", i.e. in the database of the object importing the category
         solve(B).
 
@@ -30 +30 @@
 
     :- info([
-        version is 1.0,
-        date is 2004/5/2,
+        version is 1.1,
+        date is 2008/10/2,
         author is 'Paulo Moura',
         comment is 'Meta-interpreter for pure Prolog with only conjunctions as clause bodies.']).
@@ -48 +48 @@
         proof_tree(B, PB).
     proof_tree(A, (A :- PB)) :-
-        ::clause(A, B),
+        clause(A, B),   % retrieves clauses in "this", i.e. in the database of the object importing the category
         proof_tree(B, PB).
 
@@ -57 +57 @@
 
     :- info([
-        version is 1.0,
-        date is 2004/5/5,
+        version is 1.1,
+        date is 2008/10/2,
         author is 'Paulo Moura',
         comment is 'A simple tracer meta-interpreter for pure Prolog with only conjunctions as clause bodies.']).
@@ -79 +79 @@
     trace(A, Depth) :-
         write_trace(call, A, Depth),
-        clause(A, B),
+        clause(A, B),   % retrieves clauses in "this", i.e. in the database of the object importing the category
         Depth2 is Depth + 1,
         trace(B, Depth2),
         (   write_trace(exit, A, Depth)
-            ;
-            write_trace(redo, A, Depth),
-            fail).
+        ;   write_trace(redo, A, Depth),
+            fail
+        ).
     trace(A, Depth) :-
         write_trace(fail, A, Depth),

trunk/examples/metainterpreters/NOTES.txt

@@ -28 +28 @@
 To use a meta-interpreter with an object, simply import the corresponding 
 category.
+
+Defining meta-interpreters as categories allows the use of the built-in 
+predicate clause/2 to access the clauses of object predicates without 
+forcing these predicates to be declared public or protected. Within a 
+category, calls to the built-in predicate clause/2 retrieve clauses in 
+"this", i.e. in the database of the object importing the category. 

trunk/examples/metainterpreters/rules.lgt

@@ -8 +8 @@
 
     :- op(200,  fx, if).
-    :- op(100, xfx, then).
+    :- op(150, xfx, then).
+    :- op(100, xfy, &).
 
     prove(true) :-
         !.
-
-    prove([]) :-
-        !.
-    prove([Cond| Conds]) :-
+    prove(Cond & Conds) :-
         !,
         prove(Cond),
         prove(Conds).
-
     prove(Fact) :-
-        ::clause(Fact, true).
+        clause(Fact, true).
     prove(Conclusion) :-
-        ::clause(if Conds then Conclusion, true),
+        clause(if Conds then Conclusion, true),
         prove(Conds).
 
@@ -38 +35 @@
 
     :- op(200,  fx, if).
-    :- op(100, xfx, then).
+    :- op(150, xfx, then).
+    :- op(100, xfy, &).
 
-    if [weather(sunny), weekday(weekend), time(day)] then goto(beach).
-    if [weather(raining), weekday(weekend), time(night)] then goto(cinema).
-    if [weekday(workday), time(day)] then goto(work).
+    if weather(sunny) & weekday(weekend) & time(day) then goto(beach).
+    if weather(raining) & weekday(weekend) & time(night) then goto(cinema).
+    if weekday(workday) & time(day) then goto(work).
 
     weather(raining).