diff --git a/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java b/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
index 779ec1e161ee..57664e8d97fb 100644
--- a/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
+++ b/python/src/com/jetbrains/python/psi/impl/PyAssignmentStatementImpl.java
@@ -112,10 +112,10 @@ public class PyAssignmentStatementImpl extends PyElementImpl implements PyAssign
     }
     else if (lhs_tuple != null && rhs_target != null) { // multiple LHS, single RHS: unpacking
       //for (PyExpression tuple_elt : lhs_tuple.getElements()) map.add(new Pair<PyExpression, PyExpression>(tuple_elt, rhs_target));
-      map.addAll(FP.zip(lhs_tuple, new RepeatIterable<PyExpression>(rhs_target)));
+      map.addAll(FP.zipList(lhs_tuple, new RepeatIterable<PyExpression>(rhs_target)));
     }
     else if (lhs_tuple != null && rhs_tuple != null) { // multiple both sides: piecewise mapping
-      map.addAll(FP.zip(lhs_tuple, rhs_tuple, null, null));
+      map.addAll(FP.zipList(lhs_tuple, rhs_tuple, null, null));
     }
   }
 
diff --git a/python/src/com/jetbrains/python/toolbox/ChainIterable.java b/python/src/com/jetbrains/python/toolbox/ChainIterable.java
new file mode 100644
index 000000000000..6c9425ac1d9e
--- /dev/null
+++ b/python/src/com/jetbrains/python/toolbox/ChainIterable.java
@@ -0,0 +1,97 @@
+package com.jetbrains.python.toolbox;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Iterator;
+
+/**
+ * Iterable that splices other iterables and iterates over them sequentially.
+ * User: dcheryasov
+ * Date: Nov 20, 2009 8:01:23 AM
+ */
+public class ChainIterable<T> extends ChainedListBase<Iterable<T>> implements Iterable<T> {
+
+  public ChainIterable(@Nullable Iterable<T> initial) {
+    super(initial);
+  }
+
+  public ChainIterable() {
+    super(null);
+  }
+
+
+  public ChainIterable<T> add(Iterable<T> another) {
+    return (ChainIterable<T>)super.add(another);
+  }
+
+  /**
+   * Apply wrapper to another and add the result. Convenience to avoid cluttering code with apply() calls.
+   * @param wrapper
+   * @param another
+   * @return
+   */
+  public ChainIterable<T> addWith(FP.Lambda1<Iterable<T>, Iterable<T>> wrapper, Iterable<T> another) {
+    return (ChainIterable<T>)super.add(wrapper.apply(another));
+  }
+
+  /**
+   * Convenience: add an item wrapping it into a SingleIterable behind the scenes.
+   */
+  public ChainIterable<T> add(T item) {
+    return (ChainIterable<T>)super.add(new SingleIterable<T>(item));
+  }
+
+  /**
+   * Convenience, works without ever touching an iterator.
+   * @return true if the chain contains at least one iterable (but all iterables in the chain may happen to be empty).
+   */
+  public boolean isEmpty() {
+    return (myPayload == null);
+  }
+
+  public Iterator<T> iterator() {
+
+
+    class IterMixedIn extends ChainIterationMixin<T, Iterable<T>> {
+      IterMixedIn(ChainedListBase<Iterable<T>> link) {
+        super(link);
+      }
+
+      @Override
+      public Iterator<T> toIterator(Iterable<T> first) {
+        return first.iterator();
+      }
+    }
+    final IterMixedIn mixin = new IterMixedIn(this);
+
+
+    class Iter extends ChainedListBase<Iterable<T>> implements Iterator<T> {
+
+      Iter(ChainedListBase<Iterable<T>> piggybacked) {
+        super(piggybacked.myPayload);
+        myNext = piggybacked.myNext;
+      }
+
+      public boolean hasNext() {
+        return mixin.hasNext();
+      }
+
+      public void remove() {
+        throw new UnsupportedOperationException(); // we don't remove things
+      }
+
+      public T next() {
+        return (T)mixin.next();
+      }
+
+    }
+
+    return new Iter(this);
+
+  }
+
+  @Override
+  public String toString() {
+    return FP.fold(new FP.StringCollector<T>(), this, new StringBuilder()).toString();
+  }
+}
diff --git a/python/src/com/jetbrains/python/toolbox/ChainIterationMixin.java b/python/src/com/jetbrains/python/toolbox/ChainIterationMixin.java
new file mode 100644
index 000000000000..1db0d4a35ee2
--- /dev/null
+++ b/python/src/com/jetbrains/python/toolbox/ChainIterationMixin.java
@@ -0,0 +1,52 @@
+package com.jetbrains.python.toolbox;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Common logic of chain iterators.
+ * User: dcheryasov
+ * Date: Nov 20, 2009 9:10:39 AM
+ */
+/* explicitly not public */
+abstract class ChainIterationMixin<T, TPayload> {
+  protected ChainedListBase<TPayload> myLink; // link of the chain we're currently at
+
+  protected Iterator<T> myCurrent;
+
+  public ChainIterationMixin(ChainedListBase<TPayload> link) {
+    myLink = link;
+  }
+
+  abstract public Iterator<T> toIterator(TPayload first);
+
+  // returns either null or a non-exhausted iterator.
+  @Nullable
+  public Iterator<T> getCurrent() {
+    while ((myCurrent == null || !myCurrent.hasNext()) && myLink.hasPayload()) { // fix myCurrent
+      if (myCurrent == null) {
+        myCurrent = toIterator(myLink.myPayload);
+        assert myCurrent != null;
+      }
+      else {
+        myLink.moveOn();
+        myCurrent = null;
+      }
+    }
+    return myCurrent;
+  }
+
+  public boolean hasNext() {
+    Iterator<T> current = getCurrent();
+    return (current != null);
+  }
+
+  public T next() {
+    Iterator<T> current = getCurrent();
+    if (current != null) return current.next();
+    else throw new NoSuchElementException();
+  }
+
+}
diff --git a/python/src/com/jetbrains/python/toolbox/ChainIterator.java b/python/src/com/jetbrains/python/toolbox/ChainIterator.java
new file mode 100644
index 000000000000..f5a1cd7edc91
--- /dev/null
+++ b/python/src/com/jetbrains/python/toolbox/ChainIterator.java
@@ -0,0 +1,54 @@
+package com.jetbrains.python.toolbox;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Iterator;
+
+/**
+ * An iterator that combines several other iterators and exhaust them one by one, in chain.
+ * User: dcheryasov
+ * Date: Nov 19, 2009 3:49:38 AM
+ */
+public class ChainIterator<T> extends ChainedListBase<Iterator<T>> implements Iterator<T> {
+
+  private ChainIterationMixin<T, Iterator<T>> myMixin;
+
+  /**
+   * Creates new instance.
+   * @param initial initial iterator. If null, the new iterator is empty, use {@link #add} to add initial content.
+   */
+  public ChainIterator(@Nullable Iterator<T> initial) {
+    super(initial);
+
+    myMixin = new ChainIterationMixin<T, Iterator<T>>(this) {
+      @Override
+      public Iterator<T> toIterator(Iterator<T> first) {
+        return first;
+      }
+    };
+  }
+
+
+  /**
+   * Adds another iterator to the chain. Values from this iterator will follow the values of the iterator passed to the constructor.
+   * Adding after the iteration has started is safe. 
+   * @param another iterator to add to the end of the chain.
+   * @return self, for easy chaining.
+   */
+  public ChainIterator<T> add(Iterator<T> another) {
+    return (ChainIterator<T>)super.add(another);
+  }
+
+
+  public boolean hasNext() {
+    return myMixin.hasNext();
+  }
+
+  public T next() {
+    return myMixin.next();
+  }
+
+  public void remove() {
+    throw new UnsupportedOperationException("Cannot remove from ChainIterator");
+  }
+}
diff --git a/python/src/com/jetbrains/python/toolbox/ChainedListBase.java b/python/src/com/jetbrains/python/toolbox/ChainedListBase.java
new file mode 100644
index 000000000000..fe74be537a80
--- /dev/null
+++ b/python/src/com/jetbrains/python/toolbox/ChainedListBase.java
@@ -0,0 +1,52 @@
+package com.jetbrains.python.toolbox;
+
+/**
+ * Linked list to base chain iterators an iterables on.
+ * User: dcheryasov
+ * Date: Nov 20, 2009 9:43:02 AM
+ */
+public /*abstract */class ChainedListBase<TPayload> {
+  protected TPayload myPayload;
+  protected ChainedListBase<TPayload> myNext;
+
+  protected ChainedListBase(TPayload initial) {
+    myPayload = initial;
+  }
+
+  /**
+   * Wrap payload into a new linked list element.
+   * @param payload
+   * @return
+   */
+  /*
+  abstract protected ChainedListBase<TPayload> createInstance(TPayload payload);
+  */
+
+  /**
+   * Add another element to the end of our linked list
+   * @param another
+   * @return
+   */
+  protected ChainedListBase<TPayload> add(TPayload another) {
+    if (myPayload == null) myPayload = another;
+    else {
+      ChainedListBase<TPayload> farthest = this;
+      while (farthest.myNext != null) farthest = farthest.myNext;
+      farthest.myNext = /*createInstance*/new ChainedListBase<TPayload>(another);
+    }
+    return this;
+  }
+
+  // become to our next
+  public void moveOn() {
+    if (myNext != null) {
+      myPayload = myNext.myPayload;
+      myNext = myNext.myNext;
+    }
+    else myPayload = null; // position 'after the end'
+  }
+
+  public boolean hasPayload() {
+    return myPayload != null;
+  }
+}
diff --git a/python/src/com/jetbrains/python/toolbox/FP.java b/python/src/com/jetbrains/python/toolbox/FP.java
index 4b10c0301b65..7389568eb1d3 100644
--- a/python/src/com/jetbrains/python/toolbox/FP.java
+++ b/python/src/com/jetbrains/python/toolbox/FP.java
@@ -4,41 +4,81 @@ import com.intellij.openapi.util.Pair;
 import com.jetbrains.python.PythonDocumentationProvider;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.ArrayList;
-import java.util.Iterator;
-import java.util.List;
+import java.util.*;
 
 /**
-* Tools of functional programming, the notorious half of implementation of Lisp.
+* Tools of functional programming, the notorious half of implementation of Lisp. (And sometimes a shard or two of Haskell.)
 * User: dcheryasov
 * Date: Nov 6, 2009 10:06:50 AM
 */
 public class FP {
+  
+  private FP() {
+    // do not instantiate
+  }
+
   /**
    * [a, b,..] -> [lambda(a), lambda(b),...]
+   * Action is lazy: function is applied to source items only as soon as values are extracted from the resulting iterable. 
    * @param lambda function to apply
    * @param source list to process
-   * @param <S> type of source elements
-   * @param <R> type of result elements
    * @return list of mapped values.
    */
   @NotNull
-  public static <S, R> List<R> map(@NotNull Lambda1<S, R> lambda, @NotNull List<S> source) {
-    List<R> ret = new ArrayList<R>(source.size());
-    for (S item : source) ret.add(lambda.apply(item));
+  public static <S, R> Iterable<R> map(@NotNull final Lambda1<S, R> lambda, @NotNull final Iterable<S> source) {
+
+    return new Iterable<R>() {
+      final Iterator<S> feeder = source.iterator();
+      public Iterator<R> iterator() {
+        return new Iterator<R>() {
+
+          public boolean hasNext() {
+            return feeder.hasNext();
+          }
+
+          public R next() {
+            return lambda.apply(feeder.next());
+          }
+
+          public void remove() {
+            throw new UnsupportedOperationException("Cannot remove from map()");
+          }
+        };
+      }
+    };
+  }
+
+  /**
+   * Convenience form of {@link #map(Lambda1, Iterable)}.
+   */
+  @NotNull
+  public static <S, R> Iterable<R> map(@NotNull final Lambda1<S, R> lambda, @NotNull final S[] source) {
+    return map(lambda, Arrays.asList(source));
+  }
+
+
+  /**
+   * Same as {@link #map}, but non-lazy an returns a modifiable List.
+   */
+  public static <S, R> List<R> mapList(@NotNull final Lambda1<S, R> lambda, @NotNull final Iterable<S> source) {
+    List<R> ret = new ArrayList<R>(source instanceof Collection? ((Collection)source).size() : 10);
+    for (R what : map(lambda, source)) ret.add(what);
     return ret;
   }
 
+
   /**
    * Apply a two-argument lambda to each sequence element and an accumulator.
    * @param lambda function to apply; accumulator is the first parameter, sequence item is the second
    * @param source sequence to process
    * @param unit initial value of the accumulator (like the initial 0 for summing)
+   * @param <ItemT> type of items in the list
+   * @param <AccT> 'accumulator' type; can be same as ItemT, or reasonably different (consider ItemT=String and AccT=StringBuilder)
    * @return value of the accumulator after all the list is processed.
    */
-  public static <R> R fold(@NotNull Lambda2<R, R, R> lambda, @NotNull Iterable<R> source, @NotNull final R unit) {
-    R ret = unit;
-    for (R item : source) ret = lambda.apply(ret, item);
+  public static <AccT, ItemT> AccT fold(@NotNull Lambda2<AccT, ItemT, AccT> lambda, @NotNull Iterable<ItemT> source, @NotNull final AccT unit) {
+    AccT ret = unit;
+    for (ItemT item : source) ret = lambda.apply(ret, item);
     return ret;
   }
 
@@ -47,63 +87,94 @@ public class FP {
    * @param lambda function to apply; sequence item is the first parameter, accumulator is the second
    * @param source sequence to process
    * @param unit initial value of the accumulator (like the initial 0 for summing)
-   * @return value of the accumulator after all the sequence is processed.
+   * @param <ItemT> type of items in the list
+   * @param <AccT> 'accumulator' type
+   * @return value of the accumulator after all the list is processed.
    */
-  public static <R> R foldr(@NotNull Lambda2<R, R, R> lambda, @NotNull Iterable<R> source, @NotNull final R unit) {
-    R ret = unit;
-    for (R item : source) ret = lambda.apply(item, ret);
+  public static <AccT, ItemT> AccT foldr(@NotNull Lambda2<ItemT, AccT, AccT> lambda, @NotNull Iterable<ItemT> source, @NotNull final AccT unit) {
+    AccT ret = unit;
+    for (ItemT item : source) ret = lambda.apply(item, ret);
     return ret;
   }
 
   /**
    * Zips together two sequences: [a, b,..] + [x, y,..] -> [(a, x), (b, y),..].
    * If sequences are of different length, uses up the shortest of the sequences; the rest of the longer sequence is unused.
+   * The action is lazy: either iterable is only accessed as many times as the result.
    * @param one source of first elements
    * @param two source of second elements, possibly shorter
    * @return list of pairs of elements
    */
-  public static <R1, R2> List<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two) {
+  public static <R1, R2> Iterable<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two) {
     return zipInternal(one, two, null, null, false, false);
   }
 
+  /**
+   * Same as {@link #zip(Iterable, Iterable)}, but non-lazy and returns a modifiable List.
+   */
+  public static <R1, R2> List<Pair<R1, R2>> zipList(Iterable<R1> one, Iterable<R2> two) {
+    List<Pair<R1, R2>> ret = new ArrayList<Pair<R1, R2>>(proposeZippedListLength(one, two, false, false));
+    for (Pair<R1, R2>what : zipInternal(one, two, null, null, false, false)) ret.add(what);
+    return ret;
+  }
+
 
   /**
    * Zips together two sequences: [a, b,..] + [x, y,..] -> [(a, x), (b, y),..]. Fills missing second elements with filler.
    * Always uses up entire sequence one; if sequence two is longer, part of it is unused.
+   * The action is lazy: either iterable is only accessed as many times as the result.
    * @param one source of first elements
    * @param two source of second elements, possibly shorter
    * @param filler value to use instead of elements of sequence two if it is shorter than sequence one 
    * @return list of pairs of elements
    */
-  public static <R1, R2> List<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two, R2 filler) {
+  public static <R1, R2> Iterable<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two, R2 filler) {
     return zipInternal(one, two, null, filler, false, true);
   }
 
+  /**
+   * Same as {@link #zip(Iterable, Iterable, Object)}, but non-lazy and returns a modifiable List.
+   */
+  public static <R1, R2> List<Pair<R1, R2>> zipList(Iterable<R1> one, Iterable<R2> two, R2 filler) {
+    List<Pair<R1, R2>> ret = new ArrayList<Pair<R1, R2>>(proposeZippedListLength(one, two, false, true));
+    for (Pair<R1, R2>what : zipInternal(one, two, null, filler, false, true)) ret.add(what);
+    return ret;
+  }
+
+
   /**
    * Zips together two sequences: [a, b,..] + [x, y,..] -> [(a, x), (b, y),..]. Fills all missing elements with filler.
    * Always uses up both sequences, using the appropriate filler for elements of the shorter sequences.
+   * The action is lazy: either iterable is only accessed as many times as the result.
    * @param one sequences of first elements
    * @param two sequences of second elements, possibly shorter
    * @param filler1 value to use instead of elements of sequences one if it is shorter than list two
    * @param filler2 value to use instead of elements of sequences two if it is shorter than list one
    * @return list of pairs of elements
    */
-  public static <R1, R2> List<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two, R1 filler1, R2 filler2) {
+  public static <R1, R2> Iterable<Pair<R1, R2>> zip(Iterable<R1> one, Iterable<R2> two, R1 filler1, R2 filler2) {
     return zipInternal(one, two, filler1, filler2, true, true);
   }
 
   /**
-   * Zips two lists.
-   * @param one first elements
-   * @param two second elements
-   * @param filler1 to fill missing first elements
-   * @param filler2 to fill missing second elements
-   * @param fill1 use filler1 if list one is too short
-   * @param fill2 use filler2 if list two is too short
-   * @return zipped list
+   * Same as {@link #zip(Iterable, Iterable, Object, Object)}, but non-lazy and returns a modifiable List.
    */
-  private static <R1, R2> List<Pair<R1, R2>> zipInternal(Iterable<R1> one, Iterable<R2> two, R1 filler1, R2 filler2, boolean fill1, boolean fill2) {
-    // a boring premature optimization which tries to preallocate an array list of exactly the right size
+  public static <R1, R2> List<Pair<R1, R2>> zipList(Iterable<R1> one, Iterable<R2> two, R1 filler1, R2 filler2) {
+    List<Pair<R1, R2>> ret = new ArrayList<Pair<R1, R2>>(proposeZippedListLength(one, two, true, true));
+    for (Pair<R1, R2>what : zipInternal(one, two, filler1, filler2, true, true)) ret.add(what);
+    return ret;
+  }
+
+  /**
+   * Tries to determine the size of an array list of exactly the right size to accommodate 
+   * the result of {@link #zip(Iterable, Iterable, Object, Object)}. 
+   * @param one first iterbale
+   * @param two second iterable
+   * @param fill1 true if padding of iterable one is required 
+   * @param fill2  true if padding of iterable two is required
+   * @return size, if it can be determined, or 10 (which is the default size of ArrayList).
+   */
+  public static int proposeZippedListLength(Iterable one, Iterable two, boolean fill1, boolean fill2) {
     int size1 = 0;
     int size2 = 0;
     int approx_size = 0;
@@ -114,14 +185,53 @@ public class FP {
     if (fill1 && !fill2) approx_size = size1;
     if (!fill1 && fill2) approx_size = size2;
     if (approx_size == 0) approx_size = 10;
-    List<Pair<R1, R2>> ret = new ArrayList<Pair<R1, R2>>(approx_size);
-    // the gist
-    Iterator<R1> one_iter = one.iterator();
-    Iterator<R2> two_iter = two.iterator();
-    while (one_iter.hasNext() && two_iter.hasNext()) ret.add(new Pair<R1, R2>(one_iter.next(), two_iter.next()));
-    while (fill1 && two_iter.hasNext()) ret.add(new Pair<R1, R2>(filler1, two_iter.next()));
-    while (fill2 && one_iter.hasNext()) ret.add(new Pair<R1, R2>(one_iter.next(), filler2));
-    return ret;
+    return approx_size;
+  }
+  
+  /**
+   * Zips two lists.
+   * @param one first elements
+   * @param two second elements
+   * @param filler1 to fill missing first elements
+   * @param filler2 to fill missing second elements
+   * @param fill1 use filler1 if list one is too short
+   * @param fill2 use filler2 if list two is too short
+   * @return zipped list
+   */
+  private static <R1, R2> Iterable<Pair<R1, R2>> zipInternal(
+    Iterable<R1> one, Iterable<R2> two, final R1 filler1, final R2 filler2, final boolean fill1, final boolean fill2
+  ) {
+    final Iterator<R1> one_iter = one.iterator();
+    final Iterator<R2> two_iter = two.iterator();
+    
+    return new Iterable<Pair<R1, R2>>() {
+      public Iterator<Pair<R1, R2>> iterator() {
+        
+        return new Iterator<Pair<R1, R2>>() {
+
+          public void remove() {
+            throw new UnsupportedOperationException("Cannot remove from zip()");
+          }
+
+          public boolean hasNext() {
+            final boolean one_has = one_iter.hasNext();
+            final boolean two_has = two_iter.hasNext();
+            return (
+              one_has && two_has ||
+              fill1 && two_has ||
+              fill2 && one_has
+            );
+          }
+
+          public Pair<R1, R2> next() {
+            if (one_iter.hasNext() && two_iter.hasNext()) return new Pair<R1, R2>(one_iter.next(), two_iter.next());
+            if (fill1 && two_iter.hasNext()) return new Pair<R1, R2>(filler1, two_iter.next());
+            if (fill2 && one_iter.hasNext()) return new Pair<R1, R2>(one_iter.next(), filler2);
+            throw new NoSuchElementException();
+          }
+        }; 
+      }
+    };
   }
 
   /**
@@ -153,4 +263,15 @@ public class FP {
   public interface Lambda2<A1, A2, R> {
     R apply(A1 arg1, A2 arg2);
   }
+
+
+  /**
+   * Useful for {@link FP#fold(Lambda2, Iterable, Object) fold}ing into a string. Element's {@code .toString()} is appended to the string builder.
+   */
+  public static class StringCollector<T> implements FP.Lambda2<StringBuilder, T, StringBuilder>  {
+    public StringBuilder apply(StringBuilder builder, T arg2) {
+      return builder.append(arg2.toString());
+    }
+  }
+
 }
diff --git a/python/src/com/jetbrains/python/toolbox/SingleIterator.java b/python/src/com/jetbrains/python/toolbox/SingleIterator.java
index a02ab54c9431..dfc0148e8d37 100644
--- a/python/src/com/jetbrains/python/toolbox/SingleIterator.java
+++ b/python/src/com/jetbrains/python/toolbox/SingleIterator.java
@@ -8,12 +8,12 @@ import java.util.NoSuchElementException;
 * User: dcheryasov
 * Date: Nov 6, 2009 9:57:41 AM
 */
-class SingleIterator<T> implements Iterator<T> {
+public class SingleIterator<T> implements Iterator<T> {
 
   boolean expired;
   private T content;
 
-  SingleIterator(T content) {
+  public SingleIterator(T content) {
     this.content = content;
     expired = false;
   }
diff --git a/python/testSrc/com/jetbrains/python/toolbox/FPTest.java b/python/testSrc/com/jetbrains/python/toolbox/FPTest.java
new file mode 100644
index 000000000000..549c4840636f
--- /dev/null
+++ b/python/testSrc/com/jetbrains/python/toolbox/FPTest.java
@@ -0,0 +1,89 @@
+package com.jetbrains.python.toolbox;
+
+import junit.framework.TestCase;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * Tests basic FP stuff.
+ * User: dcheryasov
+ * Date: Nov 20, 2009 6:46:25 AM
+ */
+public class FPTest extends TestCase {
+
+  public void testMap() {
+    List<String> sequence = Arrays.asList("a", "b", "c");
+    FP.Lambda1<String, String> func = new FP.Lambda1<String, String>() {
+      public String apply(String arg) {
+        return arg.toUpperCase();
+      }
+    };
+
+    int count = 0;
+    for (String what : FP.map(func, sequence)) {
+      assertEquals(sequence.get(count).toUpperCase(), what);
+      count += 1;
+    }
+    assertEquals(sequence.size(), count);
+  }
+
+  public void testMapEmpty() {
+    List<String> sequence = Arrays.asList();
+    FP.Lambda1<String, String> func = new FP.Lambda1<String, String>() {
+      public String apply(String arg) {
+        return arg.toUpperCase();
+      }
+    };
+
+    int count = 0;
+    for (String what : FP.map(func, sequence)) {
+      count += 1; // this never happens
+    }
+    assertEquals(sequence.size(), count);
+  }
+
+  
+  public void testMapLazy() {
+    List<Float> sequence = Arrays.asList(1.0f, 2.0f, 3.0f, 0.0f);
+    FP.Lambda1<Float, Float> func = new FP.Lambda1<Float, Float>() {
+      public Float apply(Float arg) {
+        return 1.0f/arg;
+      }
+    };
+
+    int count = 0;
+    Iterator<Float> iterator = FP.map(func, sequence).iterator();
+    while (iterator.hasNext() && count < 3) { // func is applied on the fly and will not be calculated for 4th arg
+      iterator.next();
+      count += 1;
+    }
+    assertEquals(3, count);
+  }
+  
+
+  public void testFold() {
+    List<String> sequence = Arrays.asList("a", "b", "c");
+    FP.Lambda2<StringBuilder, String, StringBuilder> adder = new FP.Lambda2<StringBuilder, String, StringBuilder>() {
+      public StringBuilder apply(StringBuilder builder, String arg2) {
+        return builder.append(arg2);
+      }
+    };
+    StringBuilder result = FP.fold(adder, sequence, new StringBuilder());
+    assertEquals("abc", result.toString());
+  }
+
+  public void testFoldr() {
+    List<String> sequence = Arrays.asList("a", "b", "c");
+    FP.Lambda2<String, String, String> adder = new FP.Lambda2<String, String, String>() {
+      public String apply(String left, String right) {
+        return left + right;
+      }
+    };
+    String result = FP.foldr(adder, sequence, "");
+    assertEquals("cba", result);
+  }
+
+}
diff --git a/python/testSrc/com/jetbrains/python/toolbox/IteratorsTest.java b/python/testSrc/com/jetbrains/python/toolbox/IteratorsTest.java
new file mode 100644
index 000000000000..a7ca9c321ad4
--- /dev/null
+++ b/python/testSrc/com/jetbrains/python/toolbox/IteratorsTest.java
@@ -0,0 +1,227 @@
+package com.jetbrains.python.toolbox;
+
+import junit.framework.TestCase;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Tests all iterators and iterables.
+ * User: dcheryasov
+ * Date: Nov 20, 2009 3:42:51 AM
+ */
+public class IteratorsTest extends TestCase {
+
+  public IteratorsTest() {
+    super();
+  }
+
+  public void testSingleIterable() {
+    final String value = "foo";
+    int count = 0;
+    SingleIterable<String> tested = new SingleIterable<String>(value);
+    for (String what : tested) {
+      assertEquals(value, what);
+      count += 1;
+    }
+    assertEquals(1, count);
+  }
+
+  public void testArrayIterable() {
+    final String[] values = {"foo", "bar", "baz"};
+    int count = 0;
+    ArrayIterable<String> tested = new ArrayIterable<String>(values);
+    for (String what : tested) {
+      assertEquals(values[count], what);
+      count += 1;
+    }
+    assertEquals(values.length, count);
+  }
+
+  public void testArrayIterableEmpty() {
+    final String[] values = {};
+    int count = 0;
+    ArrayIterable<String> tested = new ArrayIterable<String>(values);
+    for (String what : tested) {
+      count += 1;
+    }
+    assertEquals(values.length, count);
+  }
+
+  public void testRepeatIterable() {
+    String value = "foo";
+    RepeatIterable<String> tested = new RepeatIterable<String>(value);
+    int count = 0;
+    int times = 10;
+    for (String what : tested) {
+      assertEquals(value, what);
+      count += 1;
+      if (count >= times) break;
+    }
+    assertEquals(times, count);
+  }
+
+  public void testChainIterableByLists() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterable<String> tested = new ChainIterable<String>(list1).add(list2).add(list3);
+    int count = 0;
+    for (String what : tested) {
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIterableEmptyFirst() {
+    List<String> list1 = Arrays.asList();
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterable<String> tested = new ChainIterable<String>(list1).add(list2).add(list3);
+    int count = 0;
+    for (String what : tested) {
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIterableEmptyLast() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList();
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterable<String> tested = new ChainIterable<String>(list1).add(list2).add(list3);
+    int count = 0;
+    for (String what : tested) {
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIterableEmptyMiddle() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList();
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterable<String> tested = new ChainIterable<String>(list1).add(list2).add(list3);
+    int count = 0;
+    for (String what : tested) {
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+
+  public void testChainIteratorBySingles() {
+    final String[] values = {"foo", "bar", "baz"};
+    SingleIterator<String> zero = new SingleIterator<String>(values[0]);
+    SingleIterator<String> one = new SingleIterator<String>(values[1]);
+    SingleIterator<String> two = new SingleIterator<String>(values[2]);
+    ChainIterator<String> tested = new ChainIterator<String>(zero).add(one).add(two);
+    int count = 0;
+    String what;
+    while (tested.hasNext()) {
+      what = tested.next();
+      assertEquals(values[count], what);
+      count += 1;
+    }
+    assertEquals(values.length, count);
+  }
+
+  public void testChainIteratorByLists() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterator<String> tested = new ChainIterator<String>(list1.iterator()).add(list2.iterator()).add(list3.iterator());
+    int count = 0;
+    String what;
+    while (tested.hasNext()) {
+      what = tested.next();
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIteratorEmptyFirst() {
+    List<String> list1 = Arrays.asList();
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterator<String> tested = new ChainIterator<String>(list1.iterator()).add(list2.iterator()).add(list3.iterator());
+    int count = 0;
+    String what;
+    while (tested.hasNext()) {
+      what = tested.next();
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIteratorEmptyLast() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList("ichi", "ni", "san");
+    List<String> list3 = Arrays.asList();
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterator<String> tested = new ChainIterator<String>(list1.iterator()).add(list2.iterator()).add(list3.iterator());
+    int count = 0;
+    String what;
+    while (tested.hasNext()) {
+      what = tested.next();
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+  public void testChainIteratorEmptyMiddle() {
+    List<String> list1 = Arrays.asList("foo", "bar", "baz");
+    List<String> list2 = Arrays.asList();
+    List<String> list3 = Arrays.asList("a", "s", "d", "f");
+    List<String> all = new ArrayList<String>();
+    all.addAll(list1);
+    all.addAll(list2);
+    all.addAll(list3);
+    ChainIterator<String> tested = new ChainIterator<String>(list1.iterator()).add(list2.iterator()).add(list3.iterator());
+    int count = 0;
+    String what;
+    while (tested.hasNext()) {
+      what = tested.next();
+      assertEquals(all.get(count), what);
+      count += 1;
+    }
+    assertEquals(all.size(), count);
+  }
+
+
+}