Revise broadcast! to support lift kwarg

involves:
-Adding `Reexport` to REQUIRE

REQUIRE

@@ -1 +1,2 @@
+Reexport
 StatsBase

perf/broadcast.jl

@@ -136,6 +136,7 @@ function profile_broadcasted_right(C1, C2, V1, V2, H1, H2, Q1, Q2)
     @time(.>>(Q2, Q1))
     # print("For DataArray{Float64}:      ")
     # @time(.>>(I2, I1))
+    nothing
 end
 
 function profile_ops_halfnulls(A1, A2, Y1, Y2, F1, F2)

src/NullableArrays.jl

@@ -1,6 +1,7 @@
 module NullableArrays
 
-    using  Base.Cartesian
+    using Reexport
+    @reexport using Base.Cartesian
 
     export NullableArray,
            NullableVector,

src/broadcast.jl

@@ -1,3 +1,85 @@
+using Base.Broadcast: check_broadcast_shape
+# using Base.Cartesian
+
+function gen_nullcheck(narrays::Int, nd::Int)
+    e_nullcheck = macroexpand(:( @nref $nd isnull_1 d->j_d_1 ))
+    for k = 2:narrays
+        isnull = symbol("isnull_$k")
+        j_d_k = symbol("j_d_$k")
+        e_isnull_k = macroexpand(:( @nref $nd $(isnull) d->$(j_d_k) ))
+        e_nullcheck = Expr(:||, e_nullcheck, e_isnull_k)
+    end
+    return e_nullcheck
+end
+
+function gen_broadcast_body(nd::Int, narrays::Int, f, lift::Bool)
+    F = Expr(:quote, f)
+    e_nullcheck = gen_nullcheck(narrays, nd)
+    if lift
+        return quote
+            # set up aliases to facilitate subsequent Base.Cartesian magic
+            B_isnull = B.isnull
+            @nexprs $narrays k->(values_k = A_k.values)
+            @nexprs $narrays k->(isnull_k = A_k.isnull)
+            # check size
+            @assert ndims(B) == $nd
+            @ncall $narrays Base.Broadcast.check_broadcast_shape size(B) k->A_k
+            # main loops
+            @nloops($nd, i, B,
+                d->(@nexprs $narrays k->(j_d_k = size(A_k, d) == 1 ? 1 : i_d)), # pre
+                begin # body
+                    if $e_nullcheck
+                        @inbounds (@nref $nd B_isnull i) = true
+                    else
+                        @nexprs $narrays k->(@inbounds v_k = @nref $nd values_k d->j_d_k)
+                        @inbounds (@nref $nd B i) = (@ncall $narrays $F v)
+                    end
+                end
+            )
+        end
+    else
+        return Base.Broadcast.gen_broadcast_body_cartesian(nd, narrays, f)
+    end
+end
+
+function gen_broadcast_function(nd::Int, narrays::Int, f::Function, lift::Bool)
+    As = [symbol("A_"*string(i)) for i = 1:narrays]
+    body = gen_broadcast_body(nd, narrays, f, lift)
+    # println(macroexpand( body ))
+    @eval let
+        local _F_
+        function _F_(B, $(As...))
+            $body
+        end
+        _F_
+    end
+end
+
+@eval let cache = Dict{Any, Dict{Bool, Dict{Int, Dict{Int, Any}}}}()
+    function Base.broadcast!(f, B::NullableArray, As::NullableArray...; lift::Bool=false)
+        nd = ndims(B)
+        narrays = length(As)
+
+        cache_f    = Base.@get! cache      f       Dict{Bool, Dict{Int, Dict{Int, Any}}}()
+        cache_lift = Base.@get! cache_f    lift    Dict{Int, Dict{Int, Any}}()
+        cache_f_na = Base.@get! cache_lift narrays Dict{Int, Any}()
+        func       = Base.@get! cache_f_na nd      gen_broadcast_function(nd, narrays, f, lift)
+
+        func(B, As...)
+        return B
+    end
+end  # let cache
+
+function Base.broadcast!(f, X::NullableArray; lift::Bool=false)
+    broacast!(f, X, X; lift=lift)
+end
+
+function Base.broadcast(f, As::NullableArray...;lift::Bool=false)
+    return broadcast!(f, NullableArray(eltype(Base.promote_eltype(As...)),
+                                       Base.Broadcast.broadcast_shape(As...)),
+                      As...; lift=lift)
+end
+
 #----- broadcasted binary operations -----------------------------------------#
 
 # The following require specialized implementations because the base/broadcast