Should empty sum (and product) be defined?

Internals & Design
1 
julia> sum([1 2])
3

julia> sum([]) # from math = 0 "by convention"
ERROR: MethodError: no method matching zero(::Type{Any})
Closest candidates are:
  zero(::Type{Base.LibGit2.Oid}) at libgit2/oid.jl:88
  zero(::Type{Base.Pkg.Resolve.VersionWeights.VWPreBuildItem}) at pkg/resolve/versionweight.jl:80
  zero(::Type{Base.Pkg.Resolve.VersionWeights.VWPreBuild}) at pkg/resolve/versionweight.jl:120
  ...
 in _mapreduce(::Base.#identity, ::Base.#+, ::Base.LinearFast, ::Array{Any,1}) at ./reduce.jl:148
 in sum(::Array{Any,1}) at ./reduce.jl:229

julia> sum((1, 2))
3

julia> sum((1,))
1

julia> sum((,))
ERROR: syntax: unexpected ,

julia> sum(())
ERROR: StackOverflowError:
 in convert(::Type{Union{}}, ::Int64) at ./sysimg.jl:55 (repeats 80000 times)

I can see that maybe you want an error. Just not sure.

Not sure how you do the product, but it is defined as 1.

2

This has already been discussed, see https://github.com/JuliaLang/julia/issues/8092.

Note that

julia> sum(Int[])
0

Edit: The stackoverflow is probably a bug.

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3

Note that

julia> sum(Int[])
0

I.e. it works when it is able to determine the type of the empty array.

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