Vectorize a function on a specific argument

If you're looking to extend functions where you want only the second arg vectorized, this should do it:

macro vectorize_on_2nd(S, f)
    S = esc(S); f = esc(f); N = esc(:N)
    quote
        ($f){$N}(a, x::AbstractArray{$S, $N}) =
            reshape([($f)(a, x[i]) for i in eachindex(x)], size(x))
    end
end

Used like this:

@vectorize_on_2nd Int64 myfunc

That should give you a myfunc{N}(::Any, ::AbstractArray{Int64,N}) method.