libghc-base-prelude-doc 1.2.0.1-1 / usr / share / doc / libghc-base-prelude-doc / html / base-prelude.txt

-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | The most complete prelude formed solely from the "base" package
--   
--   A library which aims to reexport all the non-conflicting and most
--   general definitions from the "base" package. This includes APIs for
--   applicatives, arrows, monoids, foldables, traversables, exceptions,
--   generics, ST, MVars and STM.
--   
--   This package will never have any dependencies other than "base".
--   
--   <i>Versioning policy</i>
--   
--   The versioning policy of this package deviates from PVP in the sense
--   that its exports in part are transitively determined by the version of
--   "base". Therefore it's recommended for the users of "base-prelude" to
--   specify the bounds of "base" as well.
@package base-prelude
@version 1.2.0.1


-- | This module reexports most of the definitions from the "base" package,
--   which are meant to be imported unqualified.
--   
--   For details check out the source.
module BasePrelude

-- | Case analysis for the <a>Bool</a> type. <tt><a>bool</a> x y p</tt>
--   evaluates to <tt>x</tt> when <tt>p</tt> is <a>False</a>, and evaluates
--   to <tt>y</tt> when <tt>p</tt> is <a>True</a>.
--   
--   This is equivalent to <tt>if p then y else x</tt>; that is, one can
--   think of it as an if-then-else construct with its arguments reordered.
--   
--   <h4><b>Examples</b></h4>
--   
--   Basic usage:
--   
--   <pre>
--   &gt;&gt;&gt; bool "foo" "bar" True
--   "bar"
--   
--   &gt;&gt;&gt; bool "foo" "bar" False
--   "foo"
--   </pre>
--   
--   Confirm that <tt><a>bool</a> x y p</tt> and <tt>if p then y else
--   x</tt> are equivalent:
--   
--   <pre>
--   &gt;&gt;&gt; let p = True; x = "bar"; y = "foo"
--   
--   &gt;&gt;&gt; bool x y p == if p then y else x
--   True
--   
--   &gt;&gt;&gt; let p = False
--   
--   &gt;&gt;&gt; bool x y p == if p then y else x
--   True
--   </pre>
bool :: a -> a -> Bool -> a

-- | <a>&amp;</a> is a reverse application operator. This provides
--   notational convenience. Its precedence is one higher than that of the
--   forward application operator <a>$</a>, which allows <a>&amp;</a> to be
--   nested in <a>$</a>.
(&) :: a -> (a -> b) -> b
infixl 1 &

-- | Flipped version of <a>&lt;$</a>.
--   
--   <h4><b>Examples</b></h4>
--   
--   Replace the contents of a <tt><tt>Maybe</tt> <tt>Int</tt></tt> with a
--   constant <tt>String</tt>:
--   
--   <pre>
--   &gt;&gt;&gt; Nothing $&gt; "foo"
--   Nothing
--   
--   &gt;&gt;&gt; Just 90210 $&gt; "foo"
--   Just "foo"
--   </pre>
--   
--   Replace the contents of an <tt><tt>Either</tt> <tt>Int</tt>
--   <tt>Int</tt></tt> with a constant <tt>String</tt>, resulting in an
--   <tt><tt>Either</tt> <tt>Int</tt> <tt>String</tt></tt>:
--   
--   <pre>
--   &gt;&gt;&gt; Left 8675309 $&gt; "foo"
--   Left 8675309
--   
--   &gt;&gt;&gt; Right 8675309 $&gt; "foo"
--   Right "foo"
--   </pre>
--   
--   Replace each element of a list with a constant <tt>String</tt>:
--   
--   <pre>
--   &gt;&gt;&gt; [1,2,3] $&gt; "foo"
--   ["foo","foo","foo"]
--   </pre>
--   
--   Replace the second element of a pair with a constant <tt>String</tt>:
--   
--   <pre>
--   &gt;&gt;&gt; (1,2) $&gt; "foo"
--   (1,"foo")
--   </pre>
($>) :: Functor f => f a -> b -> f b
infixl 4 $>

-- | The <a>isSubsequenceOf</a> function takes two lists and returns
--   <a>True</a> if all the elements of the first list occur, in order, in
--   the second. The elements do not have to occur consecutively.
--   
--   <tt><a>isSubsequenceOf</a> x y</tt> is equivalent to <tt><a>elem</a> x
--   (<a>subsequences</a> y)</tt>.
--   
--   <h4><b>Examples</b></h4>
--   
--   <pre>
--   &gt;&gt;&gt; isSubsequenceOf "GHC" "The Glorious Haskell Compiler"
--   True
--   
--   &gt;&gt;&gt; isSubsequenceOf ['a','d'..'z'] ['a'..'z']
--   True
--   
--   &gt;&gt;&gt; isSubsequenceOf [1..10] [10,9..0]
--   False
--   </pre>
isSubsequenceOf :: Eq a => [a] -> [a] -> Bool

-- | Sort a list by comparing the results of a key function applied to each
--   element. <tt>sortOn f</tt> is equivalent to <tt>sortBy (comparing
--   f)</tt>, but has the performance advantage of only evaluating
--   <tt>f</tt> once for each element in the input list. This is called the
--   decorate-sort-undecorate paradigm, or Schwartzian transform.
sortOn :: Ord b => (a -> b) -> [a] -> [a]

-- | Decompose a list into its head and tail. If the list is empty, returns
--   <a>Nothing</a>. If the list is non-empty, returns <tt><a>Just</a> (x,
--   xs)</tt>, where <tt>x</tt> is the head of the list and <tt>xs</tt> its
--   tail.
uncons :: [a] -> Maybe (a, [a])

-- | Like <a>traceShow</a> but returns the shown value instead of a third
--   value.
traceShowId :: Show a => a -> a

-- | Like <a>trace</a> but returning unit in an arbitrary
--   <a>Applicative</a> context. Allows for convenient use in do-notation.
--   
--   Note that the application of <a>traceM</a> is not an action in the
--   <a>Applicative</a> context, as <a>traceIO</a> is in the <a>IO</a>
--   type. While the fresh bindings in the following example will force the
--   <a>traceM</a> expressions to be reduced every time the
--   <tt>do</tt>-block is executed, <tt>traceM "not crashed"</tt> would
--   only be reduced once, and the message would only be printed once. If
--   your monad is in <tt>MonadIO</tt>, <tt>liftIO . traceIO</tt> may be a
--   better option.
--   
--   <pre>
--   ... = do
--     x &lt;- ...
--     traceM $ "x: " ++ show x
--     y &lt;- ...
--     traceM $ "y: " ++ show y
--   </pre>
traceM :: Applicative f => String -> f ()

-- | Like <a>traceM</a>, but uses <a>show</a> on the argument to convert it
--   to a <a>String</a>.
--   
--   <pre>
--   ... = do
--     x &lt;- ...
--     traceShowM $ x
--     y &lt;- ...
--     traceShowM $ x + y
--   </pre>
traceShowM :: (Show a, Applicative f) => a -> f ()