Remove the hasAdvancer() approach(). Now first() and limit() of Traverser use the upstream tryAdvance(). And takeWhile() still use shortCircuit().

Author: fmcarvalho

src/main/java/org/jayield/Query.java

@@ -86,10 +86,6 @@ public Query(Advancer<T> adv, Traverser<T> trav) {
         this.trav = trav;
     }
 
-    public boolean hasAdvancer() {
-        return adv != null;
-    }
-
     /**
      * Yields elements sequentially in the current thread,
      * until all elements have been processed or an
@@ -242,8 +238,8 @@ public final Query<T> limit(int n){
      * {@link Object#equals(Object)}) of this query.
      */
     public final Query<T> distinct(){
-        AdvancerDistinct<T> adv = new AdvancerDistinct<>(this);
-        return new Query<>(adv, adv);
+        AdvancerDistinct<T> dis = new AdvancerDistinct<>(this);
+        return new Query<>(dis, dis);
     }
 
     /**
@@ -252,8 +248,8 @@ public final Query<T> distinct(){
      * the provided mapping function to each element.
      */
     public final <R> Query<R> flatMap(Function<? super T,? extends Query<? extends R>> mapper){
-        AdvancerFlatMap<T, R> adv = new AdvancerFlatMap<>(this, mapper);
-        return new Query<>(adv, adv);
+        AdvancerFlatMap<T, R> map = new AdvancerFlatMap<>(this, mapper);
+        return new Query<>(map, map);
     }
 
     /**
@@ -271,8 +267,8 @@ public final Query<T> peek(Consumer<? super T> action) {
      * this query that match the given predicate.
      */
     public final Query<T> takeWhile(Predicate<? super T> predicate){
-        AdvancerTakeWhile<T> adv = new AdvancerTakeWhile<>(this, predicate);
-        return new Query<>(adv, adv);
+        AdvancerTakeWhile<T> take = new AdvancerTakeWhile<>(this, predicate);
+        return new Query<>(take, take);
     }
 
     /**
@@ -293,10 +289,10 @@ public final <R> Query<R> then(Function<Query<T>, Advancer<R>> nextAdv, Function
      * {@code Traverser} object that is encapsulated in the resulting query.
      */
     public final <R> Query<R> then(Function<Query<T>, Traverser<R>> next) {
-        Advancer<R> adv = item -> { throw new UnsupportedOperationException(
+        Advancer<R> nextAdv = item -> { throw new UnsupportedOperationException(
             "Missing tryAdvance() implementation! Use the overloaded then() providing both Advancer and Traverser!");
         };
-        return new Query<>(adv, next.apply(this));
+        return new Query<>(nextAdv, next.apply(this));
     }
 
     /**
@@ -336,10 +332,7 @@ public void forEachRemaining(Consumer<? super T> action) {
      */
     public final Optional<T> findFirst(){
         Box<T> box = new Box<>();
-        this.shortCircuit(item -> {
-            box.turnPresent(item);
-            Yield.bye();
-        });
+        this.tryAdvance(box::turnPresent);
         return box.isPresent()
                 ? Optional.of(box.getValue())
                 : Optional.empty();

src/main/java/org/jayield/advs/AdvancerDropWhile.java

@@ -35,13 +35,14 @@ public boolean tryAdvance(Yield<? super T> yield) {
         if (dropped) {
             return upstream.tryAdvance(yield);
         } else {
-            Yield<T> takeWhile = item -> {
+            while(!dropped && upstream.tryAdvance(item -> {
                 if(!predicate.test(item)){
                     dropped = true;
                     yield.ret(item);
                 }
-            };
-            while(upstream.tryAdvance(takeWhile) && !dropped) { }
+            })) {
+                // Intentionally empty. Action specified on yield statement of tryAdvance().
+            }
             return dropped;
         }
     }

src/main/java/org/jayield/advs/AdvancerFlatMap.java

@@ -44,7 +44,7 @@ public void traverse(Yield<? super R> yield) {
     @Override
     public boolean tryAdvance(Yield<? super R> yield) {
         while (!src.tryAdvance(yield)) {
-            if(!upstream.tryAdvance((t) -> src = mapper.apply(t)))
+            if(!upstream.tryAdvance(t -> src = mapper.apply(t)))
                 return false;
         }
         return true;

src/main/java/org/jayield/advs/AdvancerIterate.java

@@ -33,7 +33,7 @@ public AdvancerIterate(U seed, UnaryOperator<U> f) {
 
     @Override
     public void traverse(Yield<? super U> yield) {
-        for(U curr = prev; true; prev = f.apply(prev))
+        for(U curr = prev; true; curr = f.apply(curr))
             yield.ret(curr);
     }
 

src/main/java/org/jayield/advs/AdvancerLimit.java

@@ -44,13 +44,8 @@ public boolean tryAdvance(Yield<? super T> yield) {
     public void traverse(Yield<? super T> yield) {
         if(count >= n)
             throw new IllegalStateException("Traverser has already been operated on or closed!");
-        if(upstream.hasAdvancer())
-            while(this.tryAdvance(yield)) { }
-        else
-            upstream.shortCircuit(item -> {
-                if(count >= n) Yield.bye();
-                count++;
-                yield.ret(item);
-            });
+        while(this.tryAdvance(yield)) {
+            // Intentionally empty. Action specified on yield statement of tryAdvance().
+        }
     }
 }

src/main/java/org/jayield/advs/AdvancerTakeWhile.java

@@ -49,13 +49,9 @@ public boolean tryAdvance(Yield<? super T> yield) {
 
     @Override
     public void traverse(Yield<? super T> yield) {
-        if(!hasNext)
-            throw new IllegalStateException("Traverser has already been operated on or closed!");
-        while(hasNext && upstream.tryAdvance(item -> {
-            if(!predicate.test(item))
-                hasNext = false;
-            else
-                yield.ret(item);
-        })) {}
+        upstream.shortCircuit(item -> {
+            if(!predicate.test(item)) Yield.bye();
+            yield.ret(item);
+        });
     }
 }

src/main/java/org/jayield/primitives/dbl/DoubleQuery.java

@@ -79,10 +79,6 @@ public DoubleQuery(DoubleAdvancer adv, DoubleTraverser trav) {
         this.trav = trav;
     }
 
-    public boolean hasAdvancer() {
-        return adv != null;
-    }
-
     /**
      * Returns a sequential ordered {@code DoubleQuery} with elements
      * from the provided {@link DoubleStream} data.
@@ -262,8 +258,6 @@ public DoubleQuery skip(int n) {
      * if a reduction can be made, using the provided accumulator.
      */
     public OptionalDouble reduce(DoubleBinaryOperator accumulator) {
-        if(!hasAdvancer())
-            throw new UnsupportedOperationException("Missing Advancer on then() or provide an identity instead!");
         DoubleBox box = new DoubleBox();
         if(this.tryAdvance(box::setValue)) {
             return OptionalDouble.of(this.reduce(box.getValue(), accumulator));
@@ -472,10 +466,7 @@ public OptionalDouble findAny() {
      */
     public OptionalDouble findFirst() {
         DoubleBox box = new DoubleBox();
-        this.shortCircuit(item -> {
-            box.turnPresent(item);
-            Yield.bye();
-        });
+        this.tryAdvance(box::turnPresent);
         return box.isPresent()
                 ? OptionalDouble.of(box.getValue())
                 : OptionalDouble.empty();
@@ -567,10 +558,10 @@ public final DoubleQuery then(
      * {@code DoubleTraverser} object that is encapsulated in the resulting {@code DoubleQuery}.
      */
     public final DoubleQuery then(Function<DoubleQuery, DoubleTraverser> next) {
-        DoubleAdvancer adv = item -> { throw new UnsupportedOperationException(
+        DoubleAdvancer nextAdv = item -> { throw new UnsupportedOperationException(
             "Missing tryAdvance() implementation! Use the overloaded then() providing both Advancer and Traverser!");
         };
-        return new DoubleQuery(adv, next.apply(this));
+        return new DoubleQuery(nextAdv, next.apply(this));
     }
 
     /**

src/main/java/org/jayield/primitives/dbl/advs/DoubleAdvancerDropWhile.java

@@ -42,7 +42,9 @@ public boolean tryAdvance(DoubleYield yield) {
                     yield.ret(item);
                 }
             };
-            while(upstream.tryAdvance(takeWhile) && !dropped) { }
+            while(upstream.tryAdvance(takeWhile) && !dropped) {
+                // Intentionally empty. Action specified on yield statement of tryAdvance().
+            }
             return dropped;
         }
 

src/main/java/org/jayield/primitives/dbl/advs/DoubleAdvancerFlatMap.java

@@ -43,7 +43,7 @@ public void traverse(DoubleYield yield) {
     @Override
     public boolean tryAdvance(DoubleYield yield) {
         while (!src.tryAdvance(yield)) {
-            if(!upstream.tryAdvance((t) -> src = mapper.apply(t)))
+            if(!upstream.tryAdvance(t -> src = mapper.apply(t)))
                 return false;
         }
         return true;

src/main/java/org/jayield/primitives/dbl/advs/DoubleAdvancerLimit.java

@@ -16,7 +16,6 @@
 
 package org.jayield.primitives.dbl.advs;
 
-import org.jayield.Yield;
 import org.jayield.primitives.dbl.DoubleAdvancer;
 import org.jayield.primitives.dbl.DoubleQuery;
 import org.jayield.primitives.dbl.DoubleTraverser;
@@ -35,13 +34,11 @@ public DoubleAdvancerLimit(DoubleQuery upstream, int n) {
 
     @Override
     public void traverse(DoubleYield yield) {
-        upstream.shortCircuit(item -> {
-            if (count >= n) {
-                Yield.bye();
-            }
-            count++;
-            yield.ret(item);
-        });
+        if(count >= n)
+            throw new IllegalStateException("Traverser has already been operated on or closed!");
+        while(this.tryAdvance(yield)) {
+            // Intentionally empty. Action specified on yield statement of tryAdvance().
+        }
     }
 
     @Override