-Support for generating external Core (post-optimization) was introduced in
-GHC 5.02. The definition of external Core in this document reflects the version of
-external Core generated by the HEAD (unstable) branch of GHC as of April 21, 2008 (version 6.9), using the compiler flag
-@-fext-core@. We expect that GHC 6.10 will be consistent with this definition.
-
-GHC supports many type system extensions; the External Core printer built into GHC only supports some of them. However, External Core should be capable of representing any Haskell 98 program, and may be able to represent programs that require certain type system extensions as well.
+GHC supports many type system extensions; the External Core printer built into GHC only supports some of them. However, External Core should be capable of representing any Haskell 98 program, and may be able to represent programs that require certain type system extensions as well. If a program uses unsupported features, GHC may fail to compile it to Core when the @-fext-core@ flag is set, or GHC may successfully compile it to Core, but the external tools will not be able to typecheck or interpret it.