Changeset 4594 for trunk/examples

Timestamp:

11/19/08 09:18:27 (7 weeks ago)

Author:

pmoura

Message:

Updated the "metapredicates" example with Paul Crocker's contributions to illustrate the use of some of the meta-predicates defined in the Logtalk library.

Location:

trunk/examples/metapredicates

Files:

• closures.lgt (modified) (5 diffs)
• loader.lgt (modified) (1 diff)
• NOTES.txt (modified) (2 diffs)
• predicates.lgt (added)
• SCRIPT.txt (modified) (5 diffs)

trunk/examples/metapredicates/closures.lgt

@@ -5 +5 @@
 
 
-:- object(meta).
+:- object(metapreds).
 
     % the meta_predicate/1 directive below changes the interpretation of meta-calls on apply/2
@@ -12 +12 @@
 
     :- public(apply/2).
+    :- meta_predicate(apply(1, *)).
     :- mode(apply(+callable, ?term), zero_or_more).
-    :- meta_predicate(apply(1, *)).
 
     apply(Closure, Arg) :-      % the Logtalk compiler verifies that any closure which is a
@@ -23 +23 @@
     test_this :-
         apply(foo(X), Y),
-        write((X, Y)), nl.
+        writeq((X, Y)), nl.
 
-    foo(1, meta).
+    foo(1, metapreds).
 
 :- end_object.
 
 
-:- object(desc,
-    extends(meta)). 
+:- object(descendant,
+    extends(metapreds)).    
 
     :- public(test_self/0).     % simple predicate for testing calls to a meta-predicate
@@ -37 +37 @@
     test_self :-
         ::apply(foo(X), Y),
-        write((X, Y)), nl.
+        writeq((X, Y)), nl.
 
-    foo(2, desc).
+    foo(2, descendant).
 
 :- end_object.
@@ -49 +49 @@
                                 % defined in another object
     test_obj :-
-        meta::apply(foo(X), Y),
-        write((X, Y)), nl.
+        metapreds::apply(foo(X), Y),
+        writeq((X, Y)), nl.
 
     foo(3, test).

trunk/examples/metapredicates/loader.lgt

@@ -1 +1 @@
 
 :- initialization((
-    logtalk_load(library(types_loader), [reload(skip)]),    % allow for static binding
-    logtalk_load([closures, metapredicates]))).
+    logtalk_load([library(types_loader), library(metapredicates_loader)], [reload(skip)]),  % allow for static binding
+    logtalk_load([predicates, closures, metapredicates]))).

trunk/examples/metapredicates/NOTES.txt

@@ -16 +16 @@
 body of the predicate definition.
 
-This example defines two objects:
+This example defines the following objects:
 
     sort(_)
@@ -26 +26 @@
         this object implements a meta-predicate that is used by sort(_) to 
         trace the sorting algorithm steps
+
+    metapreds
+    descendant
+    test
+        objects used for illustrating the use of clusures as meta-arguments
+
+    predicates
+        object defining some predicates for testing meta-predicates defined 
+        in the Logtalk library

trunk/examples/metapredicates/SCRIPT.txt

@@ -16 +16 @@
 
 
-% note that "user" is a pseudo-object representing the Prolog database
-% this implies that the integer comparisons are done using the standard
+% note that "user" is a pseudo-object representing the Prolog database;
+% therefore, the integer comparisons are performed using the standard
 % Prolog built-in predicates
 
@@ -53 +53 @@
 exit: sort([4,9],[4,9])
 
-Sorted = [1,2,3,4,9] ? 
-
+Sorted = [1,2,3,4,9]
 yes
 
@@ -60 +59 @@
 % call the meta-predicate apply/2 directly:
 
-| ?- meta::test_this.
+| ?- metapreds::test_this.
 
-1, meta
-
+1, metapreds
 yes
 
@@ -69 +67 @@
 % send an apply/2 message to self:
 
-| ?- desc::test_self.
+| ?- descendant::test_self.
 
-2, desc
-
+2, descendant
 yes
 
@@ -81 +78 @@
 
 3, test
+yes
+
+
+% use the partition/4 predicate with a predicate defined in the
+% pseudo-object "user":
+
+| ?- meta::partition(even_integer, [1,2,3,4,5], Included, Excluded).
+
+Included = [2, 4]
+Excluded = [1, 3, 5]
+yes
+
+
+% use the fold_left/4 predicate with a predicate defined in the
+% pseudo-object "user":
+
+| ?- meta::fold_left(sum_squares, 0, [1,2,3], Result).
+
+Result = 34
+yes
+
+
+% use the fold_left/4 predicate with the atom_concat/3 Prolog built-in
+% predicate:
+
+| ?- meta::fold_left(atom_concat, 'PREFIX', [abc,def,ghi], Result).
+
+Result = 'PREFIXabcdefghi'
+yes
+
+| ?- meta::fold_right(atom_concat, 'SUFIX', [abc,def,ghi], Result).
+
+Result = abcdefghiSUFIX
+yes
+
+
+% use the fold_left/4 predicate with predicates defined in the object
+% "predicates":
+
+| ?- meta::fold_left(predicates::sum, 0, [1,2,3,4,5], Result).
+
+Result = 15
+yes
+
+| ?- meta::fold_left(predicates::product, 1, [1,2,3,4,5], Result).
+
+Result = 120
+yes
+
+| ?- meta::fold_left(predicates::tuple, (0,0), [(1,2), (3,4), (6,4)], Result).
+
+Result = (10, 10)
+yes
+
+
+% use the map/2-3 predicates with some Prolog built-in predicates:
+
+| ?- meta::map(integer, [1,2,3,4,5]).
 
 yes
+
+| ?- meta::map(char_code, [a,b,c,d,e], Codes).
+
+Codes = [97, 98, 99, 100, 101]
+yes