At the moment there are issues with having multiple GHC API sessions in a single executable, which boil down to GHC having global variables. A quick grep over the GHC sources shows the following instances compiler/ghci/Linker.hs:90:GLOBAL_VAR_M(v_PersistentLinkerState, ... compiler/ghci/Linker.hs:91:GLOBAL_VAR(v_InitLinkerDone, .... compiler/main/StaticFlags.hs:94:GLOBAL_VAR(v_opt_C, .... compiler/main/StaticFlags.hs:95:GLOBAL_VAR(v_opt_C_ready, .... compiler/main/DynFlags.hs:4453:GLOBAL_VAR(v_unsafeGlobalDynFlags,.... ghc/GHCi/UI.hs:149:GLOBAL_VAR(macros_ref,.... Of these the v_unsafeGlobalDynFlags can probably be ignored, as they are intended to be used in very specific, limited circumstances only. So, would it be possible to create a structure housing the remaining ones, and somehow make it possible to access these in some kind of session? Or preferably get rid of them, or move them into existing structures such as DynFlags. This is an exploratory email, more to get a handle on what has been done/considered already in this space. The issue does have a major impact on tooling developers though. Regards Alan