Module documentation for 1.6
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 7.2. A few examples:
Control.Monad.Extra.concatMapMprovides a monadic version of
concatMap, in the same way that
mapMis a monadic version of
Data.Tuple.Extra.fst3provides a function to get the first element of a triple.
Control.Exception.Extra.retryprovides a function that retries an
IOaction a number of times.
System.Environment.Extra.lookupEnvis a function available in GHC 7.6 and above. On GHC 7.6 and above this package reexports the version from
System.Environmentwhile on GHC 7.4 and below it defines an equivalent version.
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.
- I have been using most of these functions in my packages - they have proved useful enough to be worth copying/pasting into each project.
- The functions follow the spirit of the original Prelude/base libraries. I am happy to provide partial functions (e.g.
fromRight), and functions which are specialisations of more generic functions (
- Most of the functions have trivial implementations. If a beginner couldn't write the function, it probably doesn't belong here.
- I have defined only a few new data types or type aliases. It's a package for defining new utilities on existing types, not new types or concepts.
The following GHC versions correspond to the following base library versions:
- base 4.9 == GHC 8.0
- base 4.8 == GHC 7.10
- base 4.7 == GHC 7.8
- base 4.6 == GHC 7.6
- base 4.5 == GHC 7.4
- base 4.4 == GHC 7.2
A more complete list can be found here.
#23, delete subtractTime
Add readMaybe, readEither
Add errorWithoutStackTrace to Control.Exception.Extra
#25, add zipFrom and zipWithFrom
#24, add eitherToMaybe and maybeToEither
Add fromLeft' and fromRight'
Change fromLeft/fromRight signatures to follow the base libraries
Require QuickCheck 2.9
#23, deprecate offsetTimeIncrease and subtract
#22, improve offsetTime to give reliable measurements
Depend on the clock library
Add Data.Typeable.Extra containing typeRep, Proxy, (:~:)
#21, add concatForM
#11, add maybeM and eitherM
#17, change fileEq on files that do not exist to be an error
#14, add mconcatMap and mconcatMapM
#16, add fileEq
#15, add isMac
Make concatMapM/mapMaybeM faster
Make temp file functions workaround GHC bug #10731
Add stripInfix and stripInfixEnd
#9, support directory-1.2.3
Make once async exception safe
Fix a deadlock in once when two people request in parallel
Fix a missing hClose in captureOutput
#7, add nubOrd, nubOrdOn, nubOrdBy
#6, add groupSortOn and groupSortBy
#5, add splitAtEnd
Make listFilesAvoid drop trailing path separators before testing
#3, add a constraint base >= 4.4
Fix a bug in writeFileEncoding/writeFileUTF8
Fix for missing case in withNumCapabilities
Ensure barrier is thread-safe
Make subsequent signalBarrier calls throw an exception
Add timeout function
Make sure sleep never wraps round an Int
Use uncons from GHC 7.9 and above
Use the sortOn from GHC 7.9 and above
Remove getDirectoryContentsRecursive in favour of listFilesRecursive
Change the signature for newTempFile/newTempDir
Add a once function
Remove all but the extractors on triples
Remove use of ===, allows older QuickCheck versions
Fix a bug in breakEnd/spanEnd
Rename showTime to showDuration
Eliminate rep/reps, use replace instead
Switch distinct for allSame/anySame
Optimise the numeric conversions
Rename chop to repeatedly
Redo the Tuple module, additions and deletions
Add newTempFile, newTempDir
Rename strip* to trim*
Redo the cons/uncons functions
Rename withTemporaryFile to withTempFile
Change trim to strip (follow text naming convention)
Ensure operators get exported
Initial version, still unstable