For example, I would like to write a macro @macro1 that transforms
transform(df, @macro :X :Y) to
transform(df, (:X, :Y)...)
Heres' my attempt
macro macro1(ex...)
println(ex)
:($ex...)
end
transform(df, @macro1 :X :Y)
This seems quite hard. However, if allow the macro to be on the outside like this
@macro transform(df, (:X :Y))
then it's easier. But I am not sure if the "inside" macro style can achieve this.
I guess you trying to get it working with the comma?
julia> macro splicing(expr)
return Expr(:(...), esc(expr))
end
@splicing (macro with 1 method)
julia> @macroexpand tuple(:w, @splicing :x, :y)
:(tuple(:w, (:x, :y)...))
julia> tuple(:w, @splicing :x, :y)
(:w, :x, :y)
The subtle part is that the syntax @m a, b is parsed as @m((a, b)). We can just directly wrap this into the splice call.
Don't try this with actual varargs, though, nasty stack overflows can occur.
You might need a special case for input of size one, since this does not construct a tuple:
julia> tuple(:w, @splicing :x)
ERROR: MethodError: no method matching iterate(::Symbol)
Closest candidates are:
iterate(::Core.SimpleVector) at essentials.jl:600
iterate(::Core.SimpleVector, ::Any) at essentials.jl:600
iterate(::ExponentialBackOff) at error.jl:218
...
Stacktrace:
[1] top-level scope at REPL[34]:1
The following could work, but may turn out fragile:
macro splicing3(expr)
if Meta.isexpr(expr, :tuple)
return Expr(:(...), esc(expr))
else
return esc(expr)
end
end