using DataFlow: mux, interpret, interpv, ituple, ilambda, iconst, Context

function astuple(xs::Vertex)
  isconstant(xs) && isa(value(xs).value, Tuple) ? value(xs).value :
  isa(xs, Vertex) && value(xs) == tuple ? inputs(xs) :
  nothing
end

astuple(xs::Tuple) = xs

astuple(xs) = nothing

function astuples(xs)
  xs = [astuple(x) for x in xs]
  all(x->!(x==nothing), xs) ? xs : nothing
end

function imap(cb, ctx, ::typeof(map), f, xs...)
  f, xs = interpv(ctx, (f, xs))
  xs′ = astuples(xs)
  xs′ ≠ nothing ?
    group(map(f, xs′...)...) :
    cb(ctx, map, constant(f), xs...)
end

imap(f, args...) = f(args...)