roadmap.ghc-grin

# MVP

## Feature Cut
  - no exceptions
  - no threads
  - ignore / workaround problematic primops (~10 primops)
  - no GC
  - no weak pointers
  - no stable pointers
  - no STM

# Goals
  - end-to-end compiler pipeline
  - analyze / optimize programs with non problematic primops
  - report unsupported primops and features
  - codegen simple primops
  - codegen and link simple FFI


milestone todo - docs
  - pateron video
  - grin project page
  - patreon project page

milestone todo - programming
  - finalize ghc/grin pipeline
  - linking phase
  - FFI extension
  - ghc/grin test framework


small step programming TODO:
  GHC semantics:
    done - what is dynamic target? ; it's a jump to a runtime known Addr (indirect call)
    done - is ByteArray treated specially in GHC FFI codegen? YES, see: getFCallArgs
    - study Foreign Cmm codegen: StgCmmForeign.hs
    - how are coercions related to data representation?
  ghc-primop:
    done - generate primop prelude for Lambda
    done - delete state parameter from prim types i.e. MutVar s a
    done - generate primop prelude for GRIN
  STG -> Lambda:
    done - add externals for primops calls
    done - add externals for FFI calls
    done - validate if FFI calls use simple types only
    done - do not report externals as unknown
    done - eliminate wrapper primops (i.e. atomicXXX)
    done - allow ByteArray and MutableByteArray arguments as special case in FFI
    done - generate code for tagToEnum / add enough type info
    done - strip exetrnals for the whole program
    - group by kinds of used primiops (simple type / parametric / unsupported)
  Lambda -> GRIN:
    - map Ty-s properly
    - add missing types to GRIN
    - add Addr type
    - add label as Addr constant
    - linker phase