Higher-level function with variable number of parameters

Hi guys,
I need to write this kind of higher level operators op.

op ∈ {T,S,R,H,G}:   op -> indxs::Int -> params::Real -> obj::UserType  => obj::UserType

Problem I’m not able to solve is about having indxs and params of variable length.
Two arrays would be acceptable, but better no having square brackets.

Any idea? Thank you in advance!