transformers-compat: A small compatibility shim for the transformers library

[ bsd3, compatibility, library ] [ Propose Tags ]

This package includes backported versions of types that were added to transformers in transformers 0.3, 0.4, and 0.5 for users who need strict transformers 0.2 or 0.3 compatibility to run on old versions of the platform, but also need those types.

Those users should be able to just depend on transformers >= 0.2 and transformers-compat >= 0.3.

Note: missing methods are not supplied, but this at least permits the types to be used.

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Versions [faq] 0.1, 0.1.1,, 0.2, 0.3, 0.3.2, 0.3.3,,,,,,,,,,,,,,,,,,,,,,, 0.6.2, 0.6.3, 0.6.4, 0.6.5 (info)
Change log CHANGELOG.markdown
Dependencies base (>=4.3 && <5), generic-deriving (>=1.10 && <2), ghc-prim, mtl (==2.1.*), transformers (==0.3.*) [details]
License BSD-3-Clause
Copyright Copyright (C) 2012-2015 Edward A. Kmett
Author Edward A. Kmett
Maintainer Edward A. Kmett <>
Category Compatibility
Home page
Bug tracker
Source repo head: git clone git://
Uploaded by ryanglscott at Sat Mar 31 21:16:23 UTC 2018
Distributions Arch:0.6.5, Debian:0.6.2, Fedora:0.6.2, FreeBSD:, LTSHaskell:0.6.5, NixOS:0.6.5, Stackage:0.6.5, openSUSE:0.6.5
Downloads 318112 total (1030 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by rule of succession]
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Status Hackage Matrix CI
Docs pending
Build status unknown [no reports yet]


  • Control
    • Applicative
      • Control.Applicative.Backwards
      • Control.Applicative.Lift
    • Monad
      • Control.Monad.Signatures
      • Trans
        • Control.Monad.Trans.Accum
        • Control.Monad.Trans.Except
        • Control.Monad.Trans.Instances
        • Control.Monad.Trans.Select
  • Data
    • Functor
      • Data.Functor.Classes
        • Data.Functor.Classes.Generic
          • Data.Functor.Classes.Generic.Internal
      • Data.Functor.Reverse
      • Data.Functor.Sum



Use transformers 0.2. This will be selected by cabal picking the appropriate version.


Use transformers 0.3. This will be selected by cabal picking the appropriate version.


Use transformers 0.4. This will be selected by cabal picking the appropriate version.


Use transformers 0.5 up until (but not including) 0.5.3. This will be selected by cabal picking the appropriate version.

  • f-mtl Disables support for mtl for transformers 0.2 and 0.3. That is an unsupported configuration, and results in missing instances for ExceptT.

  • f-generic-deriving prevents generic-deriving from being built as a dependency. This disables certain aspects of generics for older versions of GHC. In particular, Generic(1) instances will not be backported prior to GHC 7.2, and generic operations over unlifted types will not be backported prior to GHC 8.0. This is an unsupported configuration.


Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info


Maintainer's Corner

For package maintainers and hackage trustees

Readme for transformers-compat-

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Hackage Build Status

This provides a thin compatibility shim on top of transformers-0.2 to add the types that were added in transformers-0.3.

This enables users to maintain haskell-platform compatibility, while still gaining access ot the new functionality.

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the #haskell IRC channel on

-Edward Kmett