diff --git a/Project.toml b/Project.toml
index 1f01116..0004d6d 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "Derive"
 uuid = "a07dfc7f-7d04-4eb5-84cc-a97f051f655a"
 authors = ["ITensor developers <support@itensor.org> and contributors"]
-version = "0.3.1"
+version = "0.3.2"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
diff --git a/src/abstractarrayinterface.jl b/src/abstractarrayinterface.jl
index 3586269..c6fb83a 100644
--- a/src/abstractarrayinterface.jl
+++ b/src/abstractarrayinterface.jl
@@ -92,6 +92,35 @@ end
   return error("Not implemented.")
 end
 
+@interface ::AbstractArrayInterface function Base.mapreduce(
+  f, op, as::AbstractArray...; kwargs...
+)
+  return error("Not implemented.")
+end
+
+# TODO: Generalize to multiple inputs.
+@interface interface::AbstractInterface function Base.reduce(f, a::AbstractArray; kwargs...)
+  return @interface interface mapreduce(identity, f, a; kwargs...)
+end
+
+@interface interface::AbstractArrayInterface function Base.all(a::AbstractArray)
+  return @interface interface reduce(&, a; init=true)
+end
+
+@interface interface::AbstractArrayInterface function Base.all(
+  f::Function, a::AbstractArray
+)
+  return @interface interface mapreduce(f, &, a; init=true)
+end
+
+@interface interface::AbstractArrayInterface function Base.iszero(a::AbstractArray)
+  return @interface interface all(iszero, a)
+end
+
+@interface interface::AbstractArrayInterface function Base.isreal(a::AbstractArray)
+  return @interface interface all(isreal, a)
+end
+
 @interface ::AbstractArrayInterface function Base.permutedims!(
   a_dest::AbstractArray, a_src::AbstractArray, perm
 )
diff --git a/src/interface_function.jl b/src/interface_function.jl
index ae0d0df..d34f3e5 100644
--- a/src/interface_function.jl
+++ b/src/interface_function.jl
@@ -7,11 +7,11 @@ This errors for debugging, but probably should be defined as:
 call(interface, f, args...) = f(args...)
 ```
 =#
-call(interface, f, args...) = error("Not implemented")
+call(interface, f, args...; kwargs...) = error("Not implemented")
 
 # Change the behavior of a function to use a certain interface.
 struct InterfaceFunction{Interface,F} <: Function
   interface::Interface
   f::F
 end
-(f::InterfaceFunction)(args...) = call(f.interface, f.f, args...)
+(f::InterfaceFunction)(args...; kwargs...) = call(f.interface, f.f, args...; kwargs...)
diff --git a/src/traits.jl b/src/traits.jl
index 1ee5f1b..8fffa37 100644
--- a/src/traits.jl
+++ b/src/traits.jl
@@ -19,6 +19,12 @@ function derive(::Val{:AbstractArrayOps}, type)
     Base.copy(::$type)
     Base.map(::Any, ::$type...)
     Base.map!(::Any, ::AbstractArray, ::$type...)
+    Base.mapreduce(::Any, ::Any, ::$type...; kwargs...)
+    Base.reduce(::Any, ::$type...; kwargs...)
+    Base.all(::Function, ::$type)
+    Base.all(::$type)
+    Base.iszero(::$type)
+    Base.real(::$type)
     Base.permutedims!(::Any, ::$type, ::Any)
     Broadcast.BroadcastStyle(::Type{<:$type})
     ArrayLayouts.MemoryLayout(::Type{<:$type})
diff --git a/test/basics/SparseArrayDOKs.jl b/test/basics/SparseArrayDOKs.jl
index 563f26a..44a3e32 100644
--- a/test/basics/SparseArrayDOKs.jl
+++ b/test/basics/SparseArrayDOKs.jl
@@ -10,6 +10,25 @@ function setunstoredindex!(a::AbstractArray, value, I::CartesianIndex)
   return setunstoredindex!(a, value, Tuple(I)...)
 end
 
+# A view of the stored values of an array.
+# Similar to: `@view a[collect(eachstoredindex(a))]`, but the issue
+# with that is it returns a `SubArray` wrapping a sparse array, which
+# is then interpreted as a sparse array. Also, that involves extra
+# logic for determining if the indices are stored or not, but we know
+# the indices are stored.
+struct StoredValues{T,A<:AbstractArray{T},I} <: AbstractVector{T}
+  array::A
+  storedindices::I
+end
+StoredValues(a::AbstractArray) = StoredValues(a, collect(eachstoredindex(a)))
+Base.size(a::StoredValues) = size(a.storedindices)
+Base.getindex(a::StoredValues, I::Int) = getstoredindex(a.array, a.storedindices[I])
+function Base.setindex!(a::StoredValues, value, I::Int)
+  return setstoredindex!(a.array, value, a.storedindices[I])
+end
+
+storedvalues(a::AbstractArray) = StoredValues(a)
+
 using ArrayLayouts: ArrayLayouts, MatMulMatAdd, MemoryLayout
 using Derive: Derive, @array_aliases, @derive, @interface, AbstractArrayInterface, interface
 using LinearAlgebra: LinearAlgebra
@@ -29,8 +48,8 @@ end
   a::AbstractArray{<:Any,N}, value, I::Vararg{Int,N}
 ) where {N}
   checkbounds(a, I...)
-  iszero(value) && return a
   if !isstored(a, I...)
+    iszero(value) && return a
     setunstoredindex!(a, value, I...)
     return a
   end
@@ -67,6 +86,13 @@ end
   return a_dest
 end
 
+@interface ::SparseArrayInterface function Base.mapreduce(
+  f, op, a::AbstractArray; kwargs...
+)
+  # TODO: Need to select a better `init`.
+  return mapreduce(f, op, storedvalues(a); kwargs...)
+end
+
 # ArrayLayouts functionality.
 
 function ArrayLayouts.sub_materialize(::SparseLayout, a::AbstractArray, axes::Tuple)
diff --git a/test/basics/test_basics.jl b/test/basics/test_basics.jl
index 2b4876d..581c3ef 100644
--- a/test/basics/test_basics.jl
+++ b/test/basics/test_basics.jl
@@ -72,4 +72,13 @@ elts = (Float32, Float64, Complex{Float32}, Complex{Float64})
   @test b isa SparseArrayDOK{elt,1}
   @test b == [12, 0]
   @test storedlength(b) == 1
+
+  a = SparseArrayDOK{elt}(2, 2)
+  @test iszero(a)
+  a[2, 1] = 21
+  a[1, 2] = 12
+  @test !iszero(a)
+  @test isreal(a)
+  @test sum(a) == 33
+  @test mapreduce(x -> 2x, +, a) == 66
 end