recover-rtti

Recover run-time type information from the GHC heap. The key function in this library is

classify :: a -> Either Closure (Classifier a)

which recovers type information about values about which we know nothing (in particular, no type class constraints). One example use case is the following anythingToString function:

anythingToString :: a -> String

We test that the result of anythingToString is equal to the result of regular show for a large range of data types (including user-defined ones that the library is not aware of). There are also other possible use cases; for example, it should be possible to define an anythingToJSON function.

Obviously there are limitations; the most important ones are:

• UNPACKed fields are invisible to the library. This does not need to be a major issue though, when compiling code with -O0 fields are not unpacked. (https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/exts/pragmas.html?highlight=unpack#nounpack-pragma)
• Record field names are not known, and so records are shown just using the constructor.

There may be other gotchas as well; this library is primarily intended for debugging.