:: Monoid a => [a] -> a

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!"

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.

Concatenate a monoid after reversing its elements. Used to glue together a series of textual chunks that have been accumulated "backwards".

Compose the list of ManageHooks.

concat = mconcat

List version of <>. Note that: hcat = intercalate (<>).

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.

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

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

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.

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.

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.

Version of modes without a Data context, only to be used within cmdArgsQuote.

Version of enum without a Data context, only to be used within cmdArgsQuote.

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

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

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

Extract the first element of a list, which must be non-empty.