diff --git a/.travis.yml b/.travis.yml
index d15e621..ec6516a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,20 +21,22 @@ before_install:
   - pip install --user hererocks
   - hererocks env --$LUA -rlatest    # Use latest LuaRocks, install into 'env' directory.
   - source env/bin/activate          # Add directory with all installed binaries to PATH.
+  - luarocks install luacov
+  - luarocks install luacov-coveralls --server=https://rocks.moonscript.org/dev
   # - luarocks install busted
   # - pip install cpp-coveralls
   # - luarocks install Lua-cURL         --server=https://rocks.moonscript.org/dev
-  # - luarocks install luacov-coveralls --server=https://rocks.moonscript.org/dev
   # - luarocks install lunitx
 
 install:
   - luarocks make
 
 script: 
-  - lua test.lua
+  - lua -lluacov test.lua
   # - lunit.sh test.lua
 
-#after_success:
+after_success:
+  - luacov-coveralls -v -i iter.lua -i test.impl.lua
 #  - coveralls -b .. -r .. --dump c.report.json
 #  - luacov-coveralls -j c.report.json -v
 
diff --git a/README.md b/README.md
index 0678d5f..6e16537 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 Lua Iteration Library
 ========================
 [![Build Status](https://travis-ci.org/starwing/luaiter.svg?branch=master)](https://travis-ci.org/starwing/luaiter)
+[![Coverage Status](https://coveralls.io/repos/github/starwing/luaiter/badge.svg?branch=master)](https://coveralls.io/github/starwing/luaiter?branch=master)
 
 luaiter is a rewritten version of [luafun][1]: a high-performance
 functional programming library for Lua designed with LuaJIT's trace
diff --git a/iter.lua b/iter.lua
index b4593bf..d4a98cd 100644
--- a/iter.lua
+++ b/iter.lua
@@ -1056,7 +1056,7 @@ end
 
 setmetatable(Operator, {
    __call = function(self, op)
-      return iter._(assert(self[op], "not such operator"))
+      return iter._(assert(self[op], "no such operator"))
    end
 })
 
diff --git a/test.impl.lua b/test.impl.lua
index 0c6748c..7bf7a01 100644
--- a/test.impl.lua
+++ b/test.impl.lua
@@ -142,6 +142,10 @@ for _, a in iter(1, 2, 3, 4, 5, 6, 7) do print(a) end
 attempt to iterate a number value
 --]]
 
+op"--"
+--[[ERROR
+no such operator
+--]]
 
 --! each
 
@@ -403,6 +407,24 @@ print(all(_"_1 >= 10, _1 <= 20", take(20, rand(10, 20))))
 true
 --]]
 
+local f, r = split(5, range(10))
+f:each(print)
+print '---'
+r:each(print)
+--[[OUTPUT
+1
+2
+3
+4
+5
+---
+6
+7
+8
+9
+10
+--]]
+
 
 --iter.array   = array
 --iter.resolve = resolve
@@ -644,6 +666,14 @@ iter {1,2,2,3,3,4,5} :groupby(_"_2, _2"):map(_G.unpack or table.unpack)
 5
 --]]
 
+iter {1,2,2,3,3,4,5} :group(3):map(_G.unpack or table.unpack)
+:each(print)
+--[[OUTPUT
+1,1,2,2,3,2
+4,3,5,3,6,4
+7,5
+--]]
+
 array {1,2,2,3,3,4,5} :packgroupby():flatmap(array):map(_G.unpack or table.unpack)
 :each(print)
 --[[OUTPUT
@@ -675,6 +705,14 @@ c,three
 d,nil
 --]]
 
+zip(array{"a", "b", "c", "d"}, iter{"one", "two", "three"}):each(print)
+--[[OUTPUT
+a,1,one
+b,2,two
+c,3,three
+d,nil
+--]]
+
 zipall(array{"a", "b", "c", "d"}, array{"one", "two", "three"}):each(print)
 --[[OUTPUT
 a,one
@@ -819,6 +857,35 @@ filter(_"_1 % 3 == 0", range(10)):each(print)
 9
 --]]
 
+filterout(_"_1 % 3 == 0", range(10)):each(print)
+--[[OUTPUT
+1
+2
+4
+5
+7
+8
+10
+--]]
+
+local f1,r1 = partition(_"_1 % 3 == 0", range(10))
+f1:each(print)
+print'---'
+r1:each(print)
+--[[OUTPUT
+3
+6
+9
+---
+1
+2
+4
+5
+7
+8
+10
+--]]
+
 filter(_"_1 % 3 == 0", range(0)):each(print)
 --[[OUTPUT
 --]]
@@ -880,8 +947,6 @@ Emma
 
 --! reducing
 
-eq(_.self(range(10)).reduce(op.add)(), 55)
-
 eq(range(10):map(-_1):reduce(_1+_2), -55)
 eq(foldl(_1 + _2, nil, range(5)), 15)
 eq(foldl(_1 + _2, 0, range(5)), 15)
@@ -924,6 +989,15 @@ eq(any(_1, {}), false)
 
 --! operators
 
+eq(_.self(range(10)).reduce(op.add)(), 55)
+eq(_(_1.range)(10)(_G):reduce(op.add), 55)
+_(_3)(_2, _1.._2, _.dots)("world", "hello", print, "a", "b", "c")
+print(_.andor(_.le(_1, _2), _3, _4)(1, 2, "foo", "bar"))
+--[[OUTPUT
+hello,worldhello,a,b,c
+foo
+--]]
+
 eq(op, operator) -- an alias
 
 local comparators = { 'le', 'lt', 'eq', 'ne', 'ge', 'gt' }