recover-rtti

Recover run-time type information from the GHC heap

LTS Haskell 24.27:	0.5.2
Stackage Nightly 2026-01-09:	0.5.3
Latest on Hackage:	0.5.3

See all snapshots recover-rtti appears in

BSD-3-Clause licensed by Edsko de Vries

Maintained by [email protected]

This version can be pinned in stack with:recover-rtti-0.5.3@sha256:fd9bb319fa63ae7396be6aa06a8311c2b67ef386cce859eda83f4edd25de1809,4133

Module documentation for 0.5.3

Debug
- Debug.RecoverRTTI
  - Debug.RecoverRTTI.Classify
  - Debug.RecoverRTTI.ClosureTree

Depends on 12 packages(full list with versions):

aeson, base, bytestring, containers, ghc-heap, mtl, primitive, sop-core, stm, text, unordered-containers, vector

Used by 1 package in nightly-2026-01-08(full list with versions):

skeletest

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.

Changes

Revision history for recover-rtti

0.5.3 – 2026-01-07

Support ghc-9.14 (Brandon Chinn, #48)
Support containers-0.8 (Brandon Chinn, #49)

0.5.2 – 2025-12-16

Support unordered-containers-0.2.21 (Brandon Chinn, #45)

0.5.1 – 2025-07-19

Relax bounds, including support for QuickCheck-2.16
Drop support for ghc < 9.2

0.5.0 – 2024-06-12

Support ghc 9.8 and 9.10, including bytestring 0.12
Support ByteArray and MutableByteArray
Relax bounds (Marcin Szamotulski, #38)
Drop support for ghc 8.8

0.4.3 – 2023-06-05

Support aeson 2.1, vector 0.13, and primitive 0.8 (Mitchell Rosen, #29, #35, #36)
Support bytestring 0.11.4
Support ghc 9.4 and 9.6

0.4.2 – 2023-03-23

Support mtl 2.3 (requiring at least 2.3.1) (#26). Thanks to Rebecca Turner.

0.4.1 – 2022-03-17

Support for ghc 9.2, bytestring 0.11, aeson 0.2
Added traceAnything and traceAnythingId (#13)
Added deriving-via support (AnythingToString, BoxAnything) (#3)

0.4 – 2021-06-30

Correctly set some required lower bounds.
Add support for reclassification
Add classification equality check
Add support for primitive arrays and vectors
Fix classification on OSX
General internal cleanup of the library

This release is backwards incompatible with 0.3, but users that simply use anythingToString should be unaffected.

0.3.0.0 – 2021-03-17

Fix bug that could cause anythingToString to fail on lists with an elemUserDefined exception (issue #6). Thanks to Bit Connor for the report!

0.2.1.0 – 2021-03-17

Add support for unordered-containers and boxed vectors.

0.2.0.0 – 2021-03-15

Reorganize module structure (primarily to improve Haddocks)

0.1.0.0 – 2021-03-11

Alpha release