Extra Haskell functions
A library of extra functions for the standard Haskell libraries. Most functions are simple additions, filling out missing functionality. A few functions are available in later versions of GHC, but this package makes them available back to GHC 7.10. A few examples:
Control.Monad.Extra.concatMapM
provides a monadic version of concatMap
, in the same way that mapM
is a monadic version of map
.Data.Tuple.Extra.fst3
provides a function to get the first element of a triple.Control.Exception.Extra.retry
provides a function that retries an IO
action a number of times.Data.Either.Extra.fromLeft
is a function available in GHC 8.0 and above. On GHC 8.0 and above this package reexports the version from Data.Either
while on GHC 7.10 and below it defines an equivalent version.The module Extra
documents all functions provided by this library. Modules such as Data.List.Extra
provide extra functions over Data.List
and also reexport Data.List
. Users are recommended to replace Data.List
imports with Data.List.Extra
if they need the extra functionality.
When producing a library of extra functions I have been guided by a few principles. I encourage others with small useful utility functions contribute them here, perhaps as a temporary stop before proposing they join the standard libraries.
fromRight
), and functions which are specialisations of more generic functions (whenJust
).A mapping between base
versions and GHC compiler versions can be found here.
My general contribution preferences are available here. In addition, this repo contains some generated code which is checked in, namely src/Extra.hs and test/TestGen.hs. You can generate those files by either running runghc Generate.hs
or ghci
(which uses the .ghci
file) and typing :generate
. All PR's should contain regenerated versions of those files.