Add promotion rule

Author: YingboMa

src/function_registration.jl

@@ -55,8 +55,7 @@ end
 # special cases
 Base.:^(x::Expression,y::T) where T <: Integer = Operation(Base.:^, Expression[x, y])
 Base.:^(x::Expression,y::T) where T <: Rational = Operation(Base.:^, Expression[x, y])
-Base.conj(x::Expression) = Operation(Base.conj, [x])
-Base.muladd(a::Expression, b::Expression, c::Expression) = a * b + c
 
+@register Base.conj(x)
 @register Base.getindex(x,i)
 Base.getindex(x::Operation,i::Int64) = Operation(getindex,[x,i])

src/operations.jl

@@ -66,3 +66,7 @@ Operation(x) = convert(Operation, x)
 #convert to Expr
 Base.Expr(op::Operation) = simplified_expr(op)
 Base.convert(::Type{Expr},x::Operation) = Expr(x)
+
+# promotion
+Base.promote_rule(::Type{<:Constant}, ::Type{<:Operation}) = Operation
+Base.promote_rule(::Type{<:Operation}, ::Type{<:Constant}) = Operation

test/direct.jl

@@ -82,5 +82,5 @@ function test_worldage()
 end
 test_worldage()
 
-@test muladd(x, y, z) == x * y + z
+@test_nowarn muladd(x, y, z)
 @test_nowarn [x, y, z]'