diff --git a/src/enumerable/enumerable_drop.jl b/src/enumerable/enumerable_drop.jl
index 4ee0e7c..cef74fb 100644
--- a/src/enumerable/enumerable_drop.jl
+++ b/src/enumerable/enumerable_drop.jl
@@ -1,23 +1,22 @@
-struct EnumerableDrop{T,S} <: Enumerable
+struct EnumerableDrop{S} <: Enumerable
     source::S
     n::Int
 end
 
 function drop(source::Enumerable, n::Integer)
-    T = eltype(source)
     S = typeof(source)
-    return EnumerableDrop{T,S}(source, Int(n))
+    return EnumerableDrop{S}(source, Int(n))
 end
 
-Base.iteratorsize(::Type{EnumerableDrop{T,S}}) where {T,S} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.SizeUnknown()
+Base.iteratorsize(::Type{EnumerableDrop{S}}) where {S} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.SizeUnknown()
 
-Base.eltype(iter::EnumerableDrop{T,S}) where {T,S} = T
+Base.iteratoreltype(::Type{EnumerableDrop{S}}) where {S} = Base.iteratoreltype(S)
 
-Base.eltype(::Type{EnumerableDrop{T,S}}) where {T,S} = T
+Base.eltype(::Type{EnumerableDrop{S}}) where {S} = eltype(S)
 
-Base.length(iter::EnumerableDrop{T,S}) where {T,S} = max(length(iter.source)-iter.n,0)
+Base.length(iter::EnumerableDrop{S}) where {S} = max(length(iter.source)-iter.n,0)
 
-function Base.start(iter::EnumerableDrop{T,S}) where {T,S}
+function Base.start(iter::EnumerableDrop{S}) where {S}
     source_state = start(iter.source)
     for i in 1:iter.n
         if done(iter.source, source_state)
@@ -29,10 +28,10 @@ function Base.start(iter::EnumerableDrop{T,S}) where {T,S}
     return source_state
 end
 
-function Base.next(iter::EnumerableDrop{T,S}, s) where {T,S}
+function Base.next(iter::EnumerableDrop{S}, s) where {S}
     return next(iter.source, s)
 end
 
-function Base.done(iter::EnumerableDrop{T,S}, state) where {T,S}
+function Base.done(iter::EnumerableDrop{S}, state) where {S}
     return done(iter.source, state)
 end
diff --git a/src/enumerable/enumerable_filter.jl b/src/enumerable/enumerable_filter.jl
index 7646dda..7f770da 100644
--- a/src/enumerable/enumerable_filter.jl
+++ b/src/enumerable/enumerable_filter.jl
@@ -1,41 +1,34 @@
-# T is the type of the elements produced by this iterator
-struct EnumerableFilter{T,S,Q<:Function} <: Enumerable
+# This is the HasEltype() version
+struct EnumerableFilterHasEltype{T,S,Q<:Function} <: Enumerable
     source::S
     filter::Q
 end
 
-Base.eltype(iter::EnumerableFilter{T,S,Q}) where {T,S,Q} = T
+Base.eltype(iter::EnumerableFilterHasEltype{T,S,Q}) where {T,S,Q} = T
 
-Base.eltype(iter::Type{EnumerableFilter{T,S,Q}}) where {T,S,Q} = T
+Base.eltype(iter::Type{EnumerableFilterHasEltype{T,S,Q}}) where {T,S,Q} = T
 
-struct EnumerableFilterState{T,S}
+struct EnumerableFilterHasEltypeState{T,S}
     done::Bool
     next_value::Nullable{T}
     source_state::S
 end
 
-function filter(source::Enumerable, filter_func::Function, filter_expr::Expr)
-    T = eltype(source)
-    S = typeof(source)
-    Q = typeof(filter_func)
-    return EnumerableFilter{T,S,Q}(source, filter_func)
-end
-
-function Base.start(iter::EnumerableFilter{T,S,Q}) where {T,S,Q}
+function Base.start(iter::EnumerableFilterHasEltype{T,S,Q}) where {T,S,Q}
     s = start(iter.source)
     while !done(iter.source, s)
         v,t = next(iter.source, s)
         if iter.filter(v)
-            return EnumerableFilterState(false, Nullable(v), t)
+            return EnumerableFilterHasEltypeState(false, Nullable(v), t)
         end
         s = t
     end
     # The s we return here is fake, just to make sure we
     # return something of the right type
-    return EnumerableFilterState(true, Nullable{T}(), s)
+    return EnumerableFilterHasEltypeState(true, Nullable{T}(), s)
 end
 
-function Base.next(iter::EnumerableFilter{T,S,Q}, state) where {T,S,Q}
+function Base.next(iter::EnumerableFilterHasEltype{T,S,Q}, state) where {T,S,Q}
     v = get(state.next_value)
     s = state.source_state
     while !done(iter.source,s)
@@ -44,14 +37,71 @@ function Base.next(iter::EnumerableFilter{T,S,Q}, state) where {T,S,Q}
         t = temp[2]
         if iter.filter(w)::Bool
             temp2 = Nullable(w)
-            new_state = EnumerableFilterState(false, temp2, t)
+            new_state = EnumerableFilterHasEltypeState(false, temp2, t)
             return v, new_state
         end
         s=t
     end
     # The s we return here is fake, just to make sure we
     # return something of the right type
-    v, EnumerableFilterState(true,Nullable{T}(), s)
+    v, EnumerableFilterHasEltypeState(true,Nullable{T}(), s)
+end
+
+Base.done(f::EnumerableFilterHasEltype{T,S,Q}, state) where {T,S,Q} = state.done
+
+# This is the EltypeUnknown() version
+
+struct EnumerableFilterEltypeUnknown{S,Q<:Function} <: Enumerable
+    source::S
+    filter::Q
+end
+
+Base.iteratoreltype(::Type{EnumerableFilterEltypeUnknown{S,Q}}) where {S,Q} = Base.EltypeUnknown()
+
+function Base.start(iter::EnumerableFilterEltypeUnknown{S,Q}) where {S,Q}
+    s = start(iter.source)
+    while !done(iter.source, s)
+        v,t = next(iter.source, s)
+        if iter.filter(v)
+            return (false, v, t)
+        end
+        s = t
+    end
+    return (true, )
 end
 
-Base.done(f::EnumerableFilter{T,S,Q}, state) where {T,S,Q} = state.done
+function Base.next(iter::EnumerableFilterEltypeUnknown{S,Q}, state) where {S,Q}
+    v = state[2]
+    s = state[3]
+    while !done(iter.source,s)
+        temp = next(iter.source,s)
+        w = temp[1]
+        t = temp[2]
+        if iter.filter(w)::Bool
+            return v, (false, w, t)
+        end
+        s=t
+    end
+    v, (true, v, s)
+end
+
+Base.done(f::EnumerableFilterEltypeUnknown{S,Q}, state) where {S,Q} = state[1]
+
+# Implementation of the query operator
+
+function _filter(source::Enumerable, f::Function, f_expr::Expr, ::Base.EltypeUnknown)
+    S = typeof(source)
+    Q = typeof(f)
+    return EnumerableFilterEltypeUnknown{S,Q}(source, f)
+end
+
+function _filter(source::Enumerable, f::Function, f_expr::Expr, ::Base.HasEltype)
+    T = eltype(source)
+    S = typeof(source)
+    Q = typeof(f)
+    return EnumerableFilterHasEltype{T,S,Q}(source, f)
+end
+
+function filter(source::T, filter_func::Function, filter_expr::Expr) where {T<:Enumerable}
+    return _filter(source, filter_func, filter_expr, Base.iteratoreltype(T))
+end
diff --git a/src/enumerable/enumerable_map.jl b/src/enumerable/enumerable_map.jl
index 3c6b3a2..cc1ad7b 100644
--- a/src/enumerable/enumerable_map.jl
+++ b/src/enumerable/enumerable_map.jl
@@ -1,37 +1,84 @@
-struct EnumerableMap{T, S, Q<:Function} <: Enumerable
+# This is the HasEltype() version
+
+struct EnumerableMapHasEltype{T, S, Q<:Function} <: Enumerable
     source::S
     f::Q
 end
 
-Base.iteratorsize(::Type{EnumerableMap{T,S,Q}}) where {T,S,Q} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.iteratorsize(S)
+Base.iteratorsize(::Type{EnumerableMapHasEltype{T,S,Q}}) where {T,S,Q} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.iteratorsize(S)
 
-Base.eltype(iter::EnumerableMap{T,S,Q}) where {T,S,Q} = T
+Base.eltype(iter::Type{EnumerableMapHasEltype{T,S,Q}}) where {T,S,Q} = T
 
-Base.eltype(iter::Type{EnumerableMap{T,S,Q}}) where {T,S,Q} = T
+Base.length(iter::EnumerableMapHasEltype{T,S,Q}) where {T,S,Q} = length(iter.source)
 
-Base.length(iter::EnumerableMap{T,S,Q}) where {T,S,Q} = length(iter.source)
+function Base.start(iter::EnumerableMapHasEltype{T,S,Q}) where {T,S,Q}
+    s = start(iter.source)
+    return s
+end
 
-function map(source::Enumerable, f::Function, f_expr::Expr)
-    TS = eltype(source)
-    T = Base._return_type(f, Tuple{TS,})
-    S = typeof(source)
-    Q = typeof(f)
-    return EnumerableMap{T,S,Q}(source, f)
+function Base.next(iter::EnumerableMapHasEltype{T,S,Q}, s) where {T,S,Q}
+    x = next(iter.source, s)
+    v = x[1]
+    s_new = x[2]
+    v_new = iter.f(v)::T
+    return v_new, s_new
 end
 
-function Base.start(iter::EnumerableMap{T,S,Q}) where {T,S,Q}
+function Base.done(iter::EnumerableMapHasEltype{T,S,Q}, state) where {T,S,Q}
+    return done(iter.source, state)
+end
+
+# This is the EltypeUnknown() version
+
+struct EnumerableMapEltypeUnknown{S, Q<:Function} <: Enumerable
+    source::S
+    f::Q
+end
+
+Base.iteratorsize(::Type{EnumerableMapEltypeUnknown{S,Q}}) where {S,Q} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.iteratorsize(S)
+
+Base.iteratoreltype(::Type{EnumerableMapEltypeUnknown{S,Q}}) where {S,Q} = Base.EltypeUnknown()
+
+Base.length(iter::EnumerableMapEltypeUnknown) = length(iter.source)
+
+function Base.start(iter::EnumerableMapEltypeUnknown)
     s = start(iter.source)
     return s
 end
 
-function Base.next(iter::EnumerableMap{T,S,Q}, s) where {T,S,Q}
+function Base.next(iter::EnumerableMapEltypeUnknown, s)
     x = next(iter.source, s)
     v = x[1]
     s_new = x[2]
-    v_new = iter.f(v)::T
+    v_new = iter.f(v)
     return v_new, s_new
 end
 
-function Base.done(iter::EnumerableMap{T,S,Q}, state) where {T,S,Q}
+function Base.done(iter::EnumerableMapEltypeUnknown, state)
     return done(iter.source, state)
 end
+
+# Implementation of the query operator
+
+function _map(source::Enumerable, f::Function, f_expr::Expr, ::Base.EltypeUnknown)
+    S = typeof(source)
+    Q = typeof(f)
+    return EnumerableMapEltypeUnknown{S,Q}(source, f)
+end
+
+function _map(source::Enumerable, f::Function, f_expr::Expr, ::Base.HasEltype)
+    TS = eltype(source)
+    T = Base._return_type(f, Tuple{TS,})
+    if isleaftype(T)
+        S = typeof(source)
+        Q = typeof(f)
+        return EnumerableMapHasEltype{T,S,Q}(source, f)
+    else
+        _map(source, f, f_expr, Base.EltypeUnknown())
+    end
+end
+
+function map(source::T, f::Function, f_expr::Expr) where {T<:Enumerable}
+    return _map(source, f, f_expr, Base.iteratoreltype(T))
+end
+
diff --git a/src/enumerable/enumerable_take.jl b/src/enumerable/enumerable_take.jl
index aabe22f..b91dd7e 100644
--- a/src/enumerable/enumerable_take.jl
+++ b/src/enumerable/enumerable_take.jl
@@ -1,27 +1,26 @@
-struct EnumerableTake{T,S} <: Enumerable
+struct EnumerableTake{S} <: Enumerable
     source::S
     n::Int
 end
 
 function take(source::Enumerable, n::Integer)
-    T = eltype(source)
     S = typeof(source)
-    return EnumerableTake{T,S}(source, Int(n))
+    return EnumerableTake{S}(source, Int(n))
 end
 
-Base.iteratorsize(::Type{EnumerableTake{T,S}}) where {T,S} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.SizeUnknown()
+Base.iteratorsize(::Type{EnumerableTake{S}}) where {S} = Base.iteratorsize(S) in (Base.HasLength(), Base.HasShape()) ? Base.HasLength() : Base.SizeUnknown()
 
-Base.eltype(iter::EnumerableTake{T,S}) where {T,S} = T
+Base.iteratoreltype(::Type{EnumerableTake{S}}) where {S} = Base.iteratoreltype(S)
 
-Base.eltype(::Type{EnumerableTake{T,S}}) where {T,S} = T
+Base.eltype(::Type{EnumerableTake{S}}) where {S} = eltype(S)
 
-Base.length(iter::EnumerableTake{T,S}) where {T,S} = min(length(iter.source),iter.n)
+Base.length(iter::EnumerableTake{S}) where {S} = min(length(iter.source),iter.n)
 
-function Base.start(iter::EnumerableTake{T,S}) where {T,S}
+function Base.start(iter::EnumerableTake{S}) where {S}
     return iter.n, start(iter.source)
 end
 
-function Base.next(iter::EnumerableTake{T,S}, s) where {T,S}
+function Base.next(iter::EnumerableTake{S}, s) where {S}
     n, source_state = s
     x = next(iter.source, source_state)
     v = x[1]
@@ -29,7 +28,7 @@ function Base.next(iter::EnumerableTake{T,S}, s) where {T,S}
     return v, (n-1, source_new)
 end
 
-function Base.done(iter::EnumerableTake{T,S}, state) where {T,S}
+function Base.done(iter::EnumerableTake{S}, state) where {S}
     n, source_state = state
     return n<=0 || done(iter.source, source_state)
 end
diff --git a/src/source_iterable.jl b/src/source_iterable.jl
index 3212b17..69de559 100644
--- a/src/source_iterable.jl
+++ b/src/source_iterable.jl
@@ -1,35 +1,34 @@
-struct EnumerableIterable{T,S} <: Enumerable
+struct EnumerableIterable{S} <: Enumerable
     source::S
 end
 
 function query(source)
     IteratorInterfaceExtensions.isiterable(source) || error()
     typed_source = IteratorInterfaceExtensions.getiterator(source)
-	T = eltype(typed_source)
     S = typeof(typed_source)
 
-    source_enumerable = EnumerableIterable{T,S}(typed_source)
+    source_enumerable = EnumerableIterable{S}(typed_source)
 
     return source_enumerable
 end
 
-Base.iteratorsize(::Type{EnumerableIterable{T,S}}) where {T,S} = Base.iteratorsize(S) == Base.HasShape() ? Base.HasLength() : Base.iteratorsize(S)
+Base.iteratorsize(::Type{EnumerableIterable{S}}) where {S} = Base.iteratorsize(S) == Base.HasShape() ? Base.HasLength() : Base.iteratorsize(S)
 
-Base.eltype(iter::EnumerableIterable{T,S}) where {T,S} = T
+Base.iteratoreltype(::Type{EnumerableIterable{S}}) where {S} = Base.iteratoreltype(S)
 
-Base.eltype(iter::Type{EnumerableIterable{T,S}}) where {T,S} = T
+Base.eltype(::Type{EnumerableIterable{S}}) where {S} = eltype(S)
 
-Base.length(iter::EnumerableIterable{T,S}) where {T,S} = length(iter.source)
+Base.length(iter::EnumerableIterable{S}) where {S} = length(iter.source)
 
-function Base.start(iter::EnumerableIterable{T,S}) where {T,S}
+function Base.start(iter::EnumerableIterable{S}) where {S}
     return start(iter.source)
 end
 
-@inline function Base.next(iter::EnumerableIterable{T,S}, state) where {T,S}
+@inline function Base.next(iter::EnumerableIterable{S}, state) where {S}
     return next(iter.source, state)
 end
 
-function Base.done(iter::EnumerableIterable{T,S}, state) where {T,S}
+function Base.done(iter::EnumerableIterable{S}, state) where {S}
     return done(iter.source, state)
 end
 
diff --git a/test/runtests.jl b/test/runtests.jl
index 84f0e6b..ea2a59e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -135,4 +135,7 @@ ntups = QueryOperators.query([@NT(a=1, b=2, c=3), @NT(a=4, b=5, c=6)])
 @test show(Core.CoreSTDOUT(), enum) == nothing
 @test show(Core.CoreSTDOUT(), ntups) == nothing
 
+include("test_enumerable_map.jl")
+include("test_enumerable_filter.jl")
+
 end
diff --git a/test/test_enumerable_filter.jl b/test/test_enumerable_filter.jl
new file mode 100644
index 0000000..d11210f
--- /dev/null
+++ b/test/test_enumerable_filter.jl
@@ -0,0 +1,27 @@
+using QueryOperators
+using Base.Test
+
+@testset "filter" begin
+
+X = [1,2,3,4]
+
+# Test with eltype known
+
+a = QueryOperators.@filter(QueryOperators.query(X), i->i%2==0)
+aa = collect(a)
+
+@test Base.iteratoreltype(typeof(a))==Base.HasEltype()
+@test Base.iteratorsize(typeof(a)) == Base.SizeUnknown()
+@test aa == [2,4]
+
+# Test with eltype unknown
+
+b = QueryOperators.@filter(QueryOperators.query(i for i in X), i->i%2==0)
+bb = collect(b)
+
+@test Base.iteratoreltype(typeof(b))==Base.EltypeUnknown()
+@test Base.iteratorsize(typeof(b)) == Base.SizeUnknown()
+@test bb == [2,4]
+@test eltype(bb) == Int
+
+end
diff --git a/test/test_enumerable_map.jl b/test/test_enumerable_map.jl
new file mode 100644
index 0000000..f450525
--- /dev/null
+++ b/test/test_enumerable_map.jl
@@ -0,0 +1,40 @@
+using QueryOperators
+using Base.Test
+
+@testset "map" begin
+
+X = [1,2,3,4]
+
+# Test with eltype known
+
+a = QueryOperators.@map(QueryOperators.query(X), i->i^2)
+aa = collect(a)
+
+@test Base.iteratoreltype(typeof(a))==Base.HasEltype()
+@test Base.iteratorsize(typeof(a)) == Base.HasLength()
+@test length(a) == 4
+@test aa == [1,4,9,16]
+
+# Test with eltype unknown
+
+b = QueryOperators.@map(QueryOperators.query(i for i in X), i->i)
+bb = collect(b)
+
+@test Base.iteratoreltype(typeof(b))==Base.EltypeUnknown()
+@test Base.iteratorsize(typeof(b)) == Base.HasLength()
+@test length(b) == 4
+@test bb == [1,2,3,4]
+@test eltype(bb) == Int
+
+# Test with known source eltype, but inference gives up
+
+c = QueryOperators.@map(QueryOperators.query(X), i->i>10 ? 2 : 4.)
+cc = collect(c)
+
+@test Base.iteratoreltype(typeof(c))==Base.EltypeUnknown()
+@test Base.iteratorsize(typeof(c)) == Base.HasLength()
+@test length(c) == 4
+@test cc == [4.,4.,4.,4.]
+@test eltype(cc) == Float64
+
+end