Just another update

Task/Generator-Exponential/Ruby/generator-exponential-1.rb

@@ -1,21 +1,22 @@
 # This solution cheats and uses only one generator!
 
 def powers(m)
-  return enum_for(:powers, m) unless block_given?
+  return enum_for(__method__, m) unless block_given?
 
   n = 0
   loop { yield n ** m; n += 1 }
 end
 
 def squares_without_cubes
-  return enum_for(:squares_without_cubes) unless block_given?
+  return enum_for(__method__) unless block_given?
 
   cubes = powers(3)
   c = cubes.next
   powers(2) do |s|
-    (c = cubes.next) until c >= s
+    c = cubes.next while c < s
     yield s unless c == s
   end
 end
 
 p squares_without_cubes.take(30).drop(20)
+# p squares_without_cubes.lazy.drop(20).first(10)   # Ruby 2.0+

Task/Generator-Exponential/Ruby/generator-exponential-2.rb

@@ -1,25 +1,25 @@
 # This solution uses three generators.
 
 def powers(m)
-  return enum_for(:powers, m) unless block_given?
+  return enum_for(__method__, m) unless block_given?
 
   n = 0
   loop { yield n ** m; n += 1 }
 end
 
 def squares_without_cubes
-  return enum_for(:squares_without_cubes) unless block_given?
+  return enum_for(__method__) unless block_given?
 
   cubes = powers(3)
   c = cubes.next
   squares = powers(2)
   loop do
     s = squares.next
-    (c = cubes.next) until c >= s
+    c = cubes.next while c < s
     yield s unless c == s
   end
 end
 
 answer = squares_without_cubes
 20.times { answer.next }
-p (1..10).map { answer.next }
+p 10.times.map { answer.next }

Task/Generator-Exponential/Ruby/generator-exponential-3.rb

@@ -0,0 +1,14 @@
+def filtered(s1, s2)
+  return enum_for(__method__, s1, s2) unless block_given?
+  v, f = s1.next, s2.next
+  loop do
+    v > f and f = s2.next and next
+    v < f and yield v
+    v = s1.next
+  end
+end
+
+squares, cubes = powers(2), powers(3)
+f = filtered(squares, cubes)
+p f.take(30).last(10)
+# p f.lazy.drop(20).first(10)   # Ruby 2.0+