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


-- | Run computations that depend on one or more elements in a stream.
--   
--   Run computations that depend on one or more elements in a stream.
@package withdependencies
@version 0.2.3


-- | This module is a glorified wrapper over <a>lookup</a>. It let you
--   define computations in an applicative way that "require" some optional
--   values, defined by an identifier.
--   
--   Once defined, it is possible to extract the list of identifiers, and
--   also to evaluate the computation.
--   
--   <pre>
--   let computation = ( (+) &lt;$&gt; require "a" &lt;*&gt; require "b" )
--   &gt; computeRequire M.empty computation :: Maybe Int
--   Nothing
--   &gt; computeRequire (M.fromList [("a", 12), ("b", 15)]) computation :: Maybe Int
--   Just 27
--   &gt; computeRequire (M.fromList [("a", 12), ("c", 15)]) computation :: Maybe Int
--   Nothing
--   </pre>
module Control.Dependency

-- | The main data type, used to model a computation that requires a list
--   of named parameters (the "identifier"), that are linked to a
--   "content", and that will yield a result of type "a".
data Require identifier content a

-- | This operator let you "require" a value in a computation.
require :: Eq identifier => identifier -> Require identifier content content
requireFilter :: (identifier -> Bool) -> Require identifier content (identifier, content)

-- | Evaluate a computation, given a map of key/values for possible
--   parameters.
computeRequire :: (Ord identifier, Eq identifier, Applicative f, Alternative f) => [(identifier, content)] -> Require identifier content a -> f a

-- | Checks if a computation can be completed given a set of known
--   identifiers.
isComputable :: (Ord identifier, Eq identifier) => Set identifier -> Require identifier content a -> Bool
triggersAnalyzer :: identifier -> Require identifier content a -> Bool
instance GHC.Base.Functor (Control.Dependency.Require identifier content)
instance GHC.Base.Applicative (Control.Dependency.Require identifier content)
instance GHC.Base.Alternative (Control.Dependency.Require identifier content)


-- | Runs computations depending on some values coming from a conduit. The
--   computations are defined in applicative fashion.
--   
--   <pre>
--   test :: IO [Int]
--   test = inp =$ cnd $$ CL.consume
--       where
--           inp = sourceDirectory "/etc"
--           cnd :: Conduit String IO Int
--           cnd = withRequirement (map Once comps) id (fmap length . readFile)
--           comps :: [Require String Int Int]
--           comps = [ (+) &lt;$&gt; require "/etc/passwd" &lt;*&gt; require "/etc/passwd"
--                   , (-) &lt;$&gt; require "/etc/resolv.conf" &lt;*&gt; require "/etc/nonexistent"
--                   , require "/etc/hosts"
--                   ]
--   </pre>
module Data.Conduit.Require

-- | Given a stream of values, from which an identifier and a content can
--   be extracted, runs a list of computation that depend on these.
--   
--   Each computation's output is <a>yield</a>ed downstream.
--   
--   When all computations have been run, the conduit finishes processing.
withRequirement :: (Ord identifier, Eq identifier, Monad m, Functor m) => [(RunMode, Require identifier content x)] -> (a -> identifier) -> (a -> m content) -> Conduit a m x

-- | This allows the user to parameter what happends once a requirement is
--   fulfilled.
data RunMode

-- | The requirement will be reset, and can be run multiple times
Reset :: RunMode

-- | The requirement can only run once
Once :: RunMode
instance GHC.Show.Show Data.Conduit.Require.RunMode