Data/Bool.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE NoImplicitPrelude #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Bool
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  experimental
    -- Portability :  portable
    --
    -- The 'Bool' type and related functions.
    --
    -----------------------------------------------------------------------------

    module Data.Bool (
       -- * Booleans
       Bool(..),
       -- ** Operations
       (&&),
       (||),
       not,
       otherwise,
       bool,
      ) where

    import GHC.Base

    -- | Case analysis for the 'Bool' type. @'bool' x y p@ evaluates to @x@
    -- when @p@ is 'False', and evaluates to @y@ when @p@ is 'True'.
    --
    -- This is equivalent to @if p then y else x@; that is, one can
    -- think of it as an if-then-else construct with its arguments
    -- reordered.
    --
    -- @since 4.7.0.0
    --
    -- ==== __Examples__
    --
    -- Basic usage:
    --
    -- >>> bool "foo" "bar" True
    -- "bar"
    -- >>> bool "foo" "bar" False
    -- "foo"
    --
    -- Confirm that @'bool' x y p@ and @if p then y else x@ are
    -- equivalent:
    --
    -- >>> let p = True; x = "bar"; y = "foo"
    -- >>> bool x y p == if p then y else x
    -- True
    -- >>> let p = False
    -- >>> bool x y p == if p then y else x
    -- True
    --
    bool :: a -> a -> Bool -> a
    bool f _ False = f
    bool _ t True  = t