Recover run-time type information from the GHC heap.

The main function in this package is classify, which looks at the GHC heap to recover type information about arbitrary values. This makes it possible for example to show any value (function anythingToString) without having any Show instance in scope, though there are other use cases as well. For example, you could use it to define an anythingToJSON function.

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.