[WIP] handle higher order binary ops of mixed types

src/higher_fwd_rules.jl

@@ -30,16 +30,16 @@ end
 # TODO: It's a bit embarassing that we need to write these out, but currently the
 # compiler is not strong enough to automatically lift the frule. Let's hope we
 # can delete these in the near future.
-function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(+)}, a::TaylorBundle{N}, b::TaylorBundle{N}) where {N}
+function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(+)}, a::TaylorBundle{N, T}, b::TaylorBundle{N, T}) where {N, T}
     TaylorBundle{N}(primal(a) + primal(b),
         map(+, a.tangent.coeffs, b.tangent.coeffs))
 end
 
-function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(+)}, a::TaylorBundle{N}, b::AbstractZeroBundle{N}) where {N}
+function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(+)}, a::TaylorBundle{N, T}, b::AbstractZeroBundle{N, T}) where {N, T}
     TaylorBundle{N}(primal(a) + primal(b), a.tangent.coeffs)
 end
 
-function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(-)}, a::TaylorBundle{N}, b::TaylorBundle{N}) where {N}
+function (∂☆ₙ::∂☆{N})(fb::AbstractZeroBundle{N, typeof(-)}, a::TaylorBundle{N, T}, b::TaylorBundle{N, T}) where {N, T}
     TaylorBundle{N}(primal(a) - primal(b),
         map(-, a.tangent.coeffs, b.tangent.coeffs))
 end

test/forward.jl

@@ -172,6 +172,27 @@ end
     end
 end
 
+@testset "binops of mixed number types" begin
+    # We have had issues with mixed number types before
+    struct StoreHalfed <: Number
+        val::Float64
+        StoreHalfed(x) = new(x/2)
+    end
+    Base.:-(x::StoreHalfed, y::Number) = 2*x.val - y
+    Base.:+(x::StoreHalfed, y::Number) = 2*x.val + y
+
+    sub_sh(a) = StoreHalfed(a) - 10*a
+    add_sh(a) = StoreHalfed(a) + 10*a
+    let var"'" = Diffractor.PrimeDerivativeFwd
+        @test add_sh'(100.0) == 11.0
+        @test add_sh''(100.0) == 0.0
+
+        @test sub_sh'(100.0) == -9.0
+        @test sub_sh''(100.0) == 0.0
+    end
+end
+
+
 
 @testset "taylor_compatible" begin
     taylor_compatible = Diffractor.taylor_compatible