TypeLits question, how to build a Type Application with Symbol index

Hello devs, I have {{{ data D (n :: Symbol) }}} in my module, and I want to obtain a type {{{ D "YAY!" }}} programmatically. Where can I find code that performs this (or something similar)? 1) I have to look up |D| in the current TyEnv (what if it is in a specific module?), 2) I have to build the type index (of kind Symbol), this involves FastString, looks non-trivial, 3) Apply 1) on 2), this is easy. Any hints welcome! Thanks and cheers, Gabor PS: some morsels I have so far: for 1) compiler/prelude/PrelNames.lhs:gHC_GENERICS = mkBaseModule (fsLit "GHC.Generics")