:: Monoid a => [a] -> a -package:basic-prelude

mconcat :: Monoid a => [a] -> a
base Prelude Data.Monoid GHC.Base, hedgehog Hedgehog.Internal.Prelude, base-compat Data.Monoid.Compat Prelude.Compat, relude Relude.Monoid, rio RIO.Prelude, validity Data.Validity, base-prelude BasePrelude, turtle Turtle, classy-prelude ClassyPrelude, Cabal-syntax Distribution.Compat.Prelude Distribution.Compat.Semigroup, universum Universum.Monoid, ihaskell IHaskellPrelude, terminfo System.Console.Terminfo.Base, basement Basement.Compat.Base Basement.Imports, numhask NumHask.Prelude, base-compat-batteries Data.Monoid.Compat, clash-prelude Clash.HaskellPrelude, HaTeX Text.LaTeX.Base Text.LaTeX.Base.Class, foundation Foundation, ghc-lib-parser GHC.Prelude.Basic, ghc-internal GHC.Internal.Base GHC.Internal.Data.Monoid, dimensional Numeric.Units.Dimensional.Prelude, rebase Rebase.Prelude, mixed-types-num Numeric.MixedTypes.PreludeHiding, xmonad-contrib XMonad.Config.Prime, constrained-categories Control.Category.Constrained.Prelude Control.Category.Hask, copilot-language Copilot.Language.Prelude, testing-feat Test.Feat.Enumerate, incipit-base Incipit.Base, LambdaHack Game.LambdaHack.Core.Prelude, cabal-install-solver Distribution.Solver.Compat.Prelude, faktory Faktory.Prelude, vcr Imports, verset Verset, yesod-paginator Yesod.Paginator.Prelude, calligraphy Calligraphy.Prelude, distribution-opensuse OpenSuse.Prelude OpenSuse.Prelude, hledger-web Hledger.Web.Import, termonad Termonad.Prelude
Fold a list using the monoid. For most types, the default definition for mconcat will be used, but the function is included in the class definition so that an optimized version can be provided for specific types. 
>>> mconcat ["Hello", " ", "Haskell", "!"]
"Hello Haskell!"
mconcat :: Monoid a => [a] -> a
ghc GHC.Prelude.Basic
concatReverse :: Monoid m => [m] -> m
attoparsec Data.Attoparsec.Internal
Concatenate a monoid after reversing its elements. Used to glue together a series of textual chunks that have been accumulated "backwards".
composeAll :: Monoid m => [m] -> m
xmonad XMonad.ManageHook, xmonad-contrib XMonad.Config.Prime
Compose the list of ManageHooks.
concat :: Monoid sig => [sig] -> sig
synthesizer-core Synthesizer.Generic.Cut Synthesizer.Generic.Signal
hcat :: Monoid s => [s] -> s
string-combinators Data.String.Combinators
List version of <>. Note that: hcat = intercalate (<>).
head :: HasCallStack => [a] -> a
base Prelude Data.List GHC.List
Warning: This is a partial function, it throws an error on empty lists. Use pattern matching, uncons or listToMaybe instead. Consider refactoring to use Data.List.NonEmpty.
last :: HasCallStack => [a] -> a
base Prelude Data.List GHC.List, protolude Protolude.Partial, relude Relude.Unsafe
Extract the last element of a list, which must be finite and non-empty. WARNING: This function is partial. Consider using unsnoc instead.

Examples

>>> last [1, 2, 3]
3

>>> last [1..]
* Hangs forever *

>>> last []
*** Exception: Prelude.last: empty list
head :: [a] -> a
lens Control.Lens.Internal.Doctest
headErr :: Partial => [a] -> a
safe Safe
Identical to head, namely that fails on an empty list. Useful to avoid the x-partial warning introduced in GHC 9.8. 
headErr [] = error "Prelude.head: empty list"
headErr [1,2,3] = 1
head :: HasCallStack => [a] -> a
hedgehog Hedgehog.Internal.Prelude, base-compat Prelude.Compat
Extract the first element of a list, which must be non-empty. 
>>> head [1, 2, 3]
1

>>> head [1..]
1

>>> head []
*** Exception: Prelude.head: empty list
WARNING: This function is partial. You can use case-matching, uncons or listToMaybe instead.
last :: HasCallStack => [a] -> a
hedgehog Hedgehog.Internal.Prelude, base-compat Prelude.Compat
Extract the last element of a list, which must be finite and non-empty. 
>>> last [1, 2, 3]
3

>>> last [1..]
* Hangs forever *

>>> last []
*** Exception: Prelude.last: empty list
WARNING: This function is partial. You can use reverse with case-matching, uncons or listToMaybe instead.
last :: HasCallStack => [a] -> a
ghc GHC.Prelude.Basic
head :: HasCallStack => [a] -> a
ghc GHC.Prelude.Basic
only :: [a] -> a
ghc GHC.Utils.Misc
Utility function to go from a singleton list to it's element. Wether or not the argument is a singleton list is only checked in debug builds.
modes# :: [a] -> a
cmdargs System.Console.CmdArgs.Quote
Version of modes without a Data context, only to be used within cmdArgsQuote.
enum# :: [a] -> a
cmdargs System.Console.CmdArgs.Quote
Version of enum without a Data context, only to be used within cmdArgsQuote.
head :: HasCallStack => [a] -> a
protolude Protolude.Partial
Extract the first element of a list, which must be non-empty.
Examples
>>> head [1, 2, 3]
1

>>> head [1..]
1

>>> head []
*** Exception: Prelude.head: empty list
unsafeHead :: HasCallStack => [a] -> a
protolude Protolude.Unsafe
unsafeLast :: HasCallStack => [a] -> a
protolude Protolude.Unsafe
head :: [a] -> a
snap-core Snap.Test
Extract the first element of a list, which must be non-empty. 
>>> head [1, 2, 3]
1

>>> head [1..]
1

>>> head []
*** Exception: Prelude.head: empty list
head :: HasCallStack => [a] -> a
relude Relude.Unsafe
Extract the first element of a list, which must be non-empty. To disable the warning about partiality put {-# OPTIONS_GHC -Wno-x-partial -Wno-unrecognised-warning-flags #-} at the top of the file. To disable it throughout a package put the same options into ghc-options section of Cabal file. To disable it in GHCi put :set -Wno-x-partial -Wno-unrecognised-warning-flags into ~/.ghci config file. See also the migration guide.
Examples
>>> head [1, 2, 3]
1

>>> head [1..]
1

>>> head []
*** Exception: Prelude.head: empty list
head :: [a] -> a
rio RIO.List.Partial
Extract the first element of a list, which must be non-empty.
last :: [a] -> a
rio RIO.List.Partial
Extract the last element of a list, which must be finite and non-empty.
last :: [a] -> a
base-prelude BasePrelude
Extract the last element of a list, which must be finite and non-empty. 
>>> last [1, 2, 3]
3

>>> last [1..]
* Hangs forever *

>>> last []
*** Exception: Prelude.last: empty list