diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,373 @@
+Mozilla Public License Version 2.0
+==================================
+
+1. Definitions
+--------------
+
+1.1. "Contributor"
+    means each individual or legal entity that creates, contributes to
+    the creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+    means the combination of the Contributions of others (if any) used
+    by a Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+    means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+    means Source Code Form to which the initial Contributor has attached
+    the notice in Exhibit A, the Executable Form of such Source Code
+    Form, and Modifications of such Source Code Form, in each case
+    including portions thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+    means
+
+    (a) that the initial Contributor has attached the notice described
+        in Exhibit B to the Covered Software; or
+
+    (b) that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the
+        terms of a Secondary License.
+
+1.6. "Executable Form"
+    means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+    means a work that combines Covered Software with other material, in
+    a separate file or files, that is not Covered Software.
+
+1.8. "License"
+    means this document.
+
+1.9. "Licensable"
+    means having the right to grant, to the maximum extent possible,
+    whether at the time of the initial grant or subsequently, any and
+    all of the rights conveyed by this License.
+
+1.10. "Modifications"
+    means any of the following:
+
+    (a) any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered
+        Software; or
+
+    (b) any new file in Source Code Form that contains any Covered
+        Software.
+
+1.11. "Patent Claims" of a Contributor
+    means any patent claim(s), including without limitation, method,
+    process, and apparatus claims, in any patent Licensable by such
+    Contributor that would be infringed, but for the grant of the
+    License, by the making, using, selling, offering for sale, having
+    made, import, or transfer of either its Contributions or its
+    Contributor Version.
+
+1.12. "Secondary License"
+    means either the GNU General Public License, Version 2.0, the GNU
+    Lesser General Public License, Version 2.1, the GNU Affero General
+    Public License, Version 3.0, or any later versions of those
+    licenses.
+
+1.13. "Source Code Form"
+    means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+    means an individual or a legal entity exercising rights under this
+    License. For legal entities, "You" includes any entity that
+    controls, is controlled by, or is under common control with You. For
+    purposes of this definition, "control" means (a) the power, direct
+    or indirect, to cause the direction or management of such entity,
+    whether by contract or otherwise, or (b) ownership of more than
+    fifty percent (50%) of the outstanding shares or beneficial
+    ownership of such entity.
+
+2. License Grants and Conditions
+--------------------------------
+
+2.1. Grants
+
+Each Contributor hereby grants You a world-wide, royalty-free,
+non-exclusive license:
+
+(a) under intellectual property rights (other than patent or trademark)
+    Licensable by such Contributor to use, reproduce, make available,
+    modify, display, perform, distribute, and otherwise exploit its
+    Contributions, either on an unmodified basis, with Modifications, or
+    as part of a Larger Work; and
+
+(b) under Patent Claims of such Contributor to make, use, sell, offer
+    for sale, have made, import, and otherwise transfer either its
+    Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+The licenses granted in Section 2.1 with respect to any Contribution
+become effective for each Contribution on the date the Contributor first
+distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+The licenses granted in this Section 2 are the only rights granted under
+this License. No additional rights or licenses will be implied from the
+distribution or licensing of Covered Software under this License.
+Notwithstanding Section 2.1(b) above, no patent license is granted by a
+Contributor:
+
+(a) for any code that a Contributor has removed from Covered Software;
+    or
+
+(b) for infringements caused by: (i) Your and any other third party's
+    modifications of Covered Software, or (ii) the combination of its
+    Contributions with other software (except as part of its Contributor
+    Version); or
+
+(c) under Patent Claims infringed by Covered Software in the absence of
+    its Contributions.
+
+This License does not grant any rights in the trademarks, service marks,
+or logos of any Contributor (except as may be necessary to comply with
+the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+No Contributor makes additional grants as a result of Your choice to
+distribute the Covered Software under a subsequent version of this
+License (see Section 10.2) or under the terms of a Secondary License (if
+permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+Each Contributor represents that the Contributor believes its
+Contributions are its original creation(s) or it has sufficient rights
+to grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+This License is not intended to limit any rights You have under
+applicable copyright doctrines of fair use, fair dealing, or other
+equivalents.
+
+2.7. Conditions
+
+Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
+in Section 2.1.
+
+3. Responsibilities
+-------------------
+
+3.1. Distribution of Source Form
+
+All distribution of Covered Software in Source Code Form, including any
+Modifications that You create or to which You contribute, must be under
+the terms of this License. You must inform recipients that the Source
+Code Form of the Covered Software is governed by the terms of this
+License, and how they can obtain a copy of this License. You may not
+attempt to alter or restrict the recipients' rights in the Source Code
+Form.
+
+3.2. Distribution of Executable Form
+
+If You distribute Covered Software in Executable Form then:
+
+(a) such Covered Software must also be made available in Source Code
+    Form, as described in Section 3.1, and You must inform recipients of
+    the Executable Form how they can obtain a copy of such Source Code
+    Form by reasonable means in a timely manner, at a charge no more
+    than the cost of distribution to the recipient; and
+
+(b) You may distribute such Executable Form under the terms of this
+    License, or sublicense it under different terms, provided that the
+    license for the Executable Form does not attempt to limit or alter
+    the recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+You may create and distribute a Larger Work under terms of Your choice,
+provided that You also comply with the requirements of this License for
+the Covered Software. If the Larger Work is a combination of Covered
+Software with a work governed by one or more Secondary Licenses, and the
+Covered Software is not Incompatible With Secondary Licenses, this
+License permits You to additionally distribute such Covered Software
+under the terms of such Secondary License(s), so that the recipient of
+the Larger Work may, at their option, further distribute the Covered
+Software under the terms of either this License or such Secondary
+License(s).
+
+3.4. Notices
+
+You may not remove or alter the substance of any license notices
+(including copyright notices, patent notices, disclaimers of warranty,
+or limitations of liability) contained within the Source Code Form of
+the Covered Software, except that You may alter any license notices to
+the extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+You may choose to offer, and to charge a fee for, warranty, support,
+indemnity or liability obligations to one or more recipients of Covered
+Software. However, You may do so only on Your own behalf, and not on
+behalf of any Contributor. You must make it absolutely clear that any
+such warranty, support, indemnity, or liability obligation is offered by
+You alone, and You hereby agree to indemnify every Contributor for any
+liability incurred by such Contributor as a result of warranty, support,
+indemnity or liability terms You offer. You may include additional
+disclaimers of warranty and limitations of liability specific to any
+jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+---------------------------------------------------
+
+If it is impossible for You to comply with any of the terms of this
+License with respect to some or all of the Covered Software due to
+statute, judicial order, or regulation then You must: (a) comply with
+the terms of this License to the maximum extent possible; and (b)
+describe the limitations and the code they affect. Such description must
+be placed in a text file included with all distributions of the Covered
+Software under this License. Except to the extent prohibited by statute
+or regulation, such description must be sufficiently detailed for a
+recipient of ordinary skill to be able to understand it.
+
+5. Termination
+--------------
+
+5.1. The rights granted under this License will terminate automatically
+if You fail to comply with any of its terms. However, if You become
+compliant, then the rights granted under this License from a particular
+Contributor are reinstated (a) provisionally, unless and until such
+Contributor explicitly and finally terminates Your grants, and (b) on an
+ongoing basis, if such Contributor fails to notify You of the
+non-compliance by some reasonable means prior to 60 days after You have
+come back into compliance. Moreover, Your grants from a particular
+Contributor are reinstated on an ongoing basis if such Contributor
+notifies You of the non-compliance by some reasonable means, this is the
+first time You have received notice of non-compliance with this License
+from such Contributor, and You become compliant prior to 30 days after
+Your receipt of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+infringement claim (excluding declaratory judgment actions,
+counter-claims, and cross-claims) alleging that a Contributor Version
+directly or indirectly infringes any patent, then the rights granted to
+You by any and all Contributors for the Covered Software under Section
+2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all
+end user license agreements (excluding distributors and resellers) which
+have been validly granted by You or Your distributors under this License
+prior to termination shall survive termination.
+
+************************************************************************
+*                                                                      *
+*  6. Disclaimer of Warranty                                           *
+*  -------------------------                                           *
+*                                                                      *
+*  Covered Software is provided under this License on an "as is"       *
+*  basis, without warranty of any kind, either expressed, implied, or  *
+*  statutory, including, without limitation, warranties that the       *
+*  Covered Software is free of defects, merchantable, fit for a        *
+*  particular purpose or non-infringing. The entire risk as to the     *
+*  quality and performance of the Covered Software is with You.        *
+*  Should any Covered Software prove defective in any respect, You     *
+*  (not any Contributor) assume the cost of any necessary servicing,   *
+*  repair, or correction. This disclaimer of warranty constitutes an   *
+*  essential part of this License. No use of any Covered Software is   *
+*  authorized under this License except under this disclaimer.         *
+*                                                                      *
+************************************************************************
+
+************************************************************************
+*                                                                      *
+*  7. Limitation of Liability                                          *
+*  --------------------------                                          *
+*                                                                      *
+*  Under no circumstances and under no legal theory, whether tort      *
+*  (including negligence), contract, or otherwise, shall any           *
+*  Contributor, or anyone who distributes Covered Software as          *
+*  permitted above, be liable to You for any direct, indirect,         *
+*  special, incidental, or consequential damages of any character      *
+*  including, without limitation, damages for lost profits, loss of    *
+*  goodwill, work stoppage, computer failure or malfunction, or any    *
+*  and all other commercial damages or losses, even if such party      *
+*  shall have been informed of the possibility of such damages. This   *
+*  limitation of liability shall not apply to liability for death or   *
+*  personal injury resulting from such party's negligence to the       *
+*  extent applicable law prohibits such limitation. Some               *
+*  jurisdictions do not allow the exclusion or limitation of           *
+*  incidental or consequential damages, so this exclusion and          *
+*  limitation may not apply to You.                                    *
+*                                                                      *
+************************************************************************
+
+8. Litigation
+-------------
+
+Any litigation relating to this License may be brought only in the
+courts of a jurisdiction where the defendant maintains its principal
+place of business and such litigation shall be governed by laws of that
+jurisdiction, without reference to its conflict-of-law provisions.
+Nothing in this Section shall prevent a party's ability to bring
+cross-claims or counter-claims.
+
+9. Miscellaneous
+----------------
+
+This License represents the complete agreement concerning the subject
+matter hereof. If any provision of this License is held to be
+unenforceable, such provision shall be reformed only to the extent
+necessary to make it enforceable. Any law or regulation which provides
+that the language of a contract shall be construed against the drafter
+shall not be used to construe this License against a Contributor.
+
+10. Versions of the License
+---------------------------
+
+10.1. New Versions
+
+Mozilla Foundation is the license steward. Except as provided in Section
+10.3, no one other than the license steward has the right to modify or
+publish new versions of this License. Each version will be given a
+distinguishing version number.
+
+10.2. Effect of New Versions
+
+You may distribute the Covered Software under the terms of the version
+of the License under which You originally received the Covered Software,
+or under the terms of any subsequent version published by the license
+steward.
+
+10.3. Modified Versions
+
+If you create software not governed by this License, and you want to
+create a new license for such software, you may create and use a
+modified version of this License if you rename the license and remove
+any references to the name of the license steward (except to note that
+such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+Licenses
+
+If You choose to distribute Source Code Form that is Incompatible With
+Secondary Licenses under the terms of this version of the License, the
+notice described in Exhibit B of this License must be attached.
+
+Exhibit A - Source Code Form License Notice
+-------------------------------------------
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular
+file, then You may include the notice in a location (such as a LICENSE
+file in a relevant directory) where a recipient would be likely to look
+for such a notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+---------------------------------------------------------
+
+  This Source Code Form is "Incompatible With Secondary Licenses", as
+  defined by the Mozilla Public License, v. 2.0.
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,5 @@
+Evaluate predicate functions against WAI requests and receive
+metadata in addition to a success/failure indicator.
+
+Predicates can be combined using logical connectives and the
+metadata are passed on accordingly.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Data/Predicate.hs b/src/Data/Predicate.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Predicate.hs
@@ -0,0 +1,134 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE TypeOperators #-}
+
+module Data.Predicate
+    ( Predicate
+    , constant
+    , failure
+    , true
+    , false
+    , and
+    , or
+    , orElse
+    , (.&.)
+    , (.|.)
+    , (|||)
+    , opt
+    , def
+    , mapResult
+    , mapOkay
+    , mapFail
+    , exec
+    , module Data.Predicate.Product
+    , module Data.Predicate.Result
+    ) where
+
+import Control.Monad
+import Data.Predicate.Product
+import Data.Predicate.Result
+import Prelude hiding (and, or)
+
+-- | A predicate is a function of some value of type @a@ to a 'Result',
+-- i.e. a 'Bool'-like value with 'Okay' as 'True' and 'Fail' as 'False',
+-- which carries additional data in each branch.
+type Predicate a f t = a -> Result f t
+
+-- | A predicate which always returns @Okay@ with the given
+-- value as metadata.
+constant :: t -> Predicate a f t
+constant t _ = return t
+
+true :: Predicate a f ()
+true = constant ()
+
+-- | A predicate which always returns @Fail@ with the given
+-- value as metadata.
+failure :: f -> Predicate a f t
+failure f _ = Fail f
+
+false :: Predicate a () t
+false = failure ()
+
+infixr 3 .&.
+infixr 2 .|.
+infixr 2 |||
+
+-- | A predicate corresponding to the logical AND connective
+-- of two predicate.
+and, (.&.) :: Predicate a f t -> Predicate a f t' -> Predicate a f (t ::: t')
+and f g x = f x `cmp` g x
+  where
+    cmp (Okay d y) (Okay w z) = Okay (d + w) (y ::: z)
+    cmp (Okay _ _) (Fail   y) = Fail y
+    cmp (Fail   y) _          = Fail y
+
+-- | A predicate corresponding to the logical
+-- OR connective of two predicates. It requires the
+-- metadata of each @Okay@ branch to be of the same type.
+--
+-- If both arguments evaluate to @Okay@ the one with the
+-- smaller \"delta\" will be preferred, or--if equal--the
+-- left-hand argument.
+or, (.|.) :: Predicate a f t -> Predicate a f t -> Predicate a f t
+or f g x = f x `cmp` g x
+  where
+    cmp a@(Okay d _) b@(Okay w _)  = if w < d then b else a
+    cmp a@(Okay _ _)   (Fail _)    = a
+    cmp (Fail _)     b@(Okay _ _)  = b
+    cmp (Fail _)     b@(Fail _)    = b
+
+-- | A predicate corresponding to the logical
+-- OR connective of two predicates. The metadata of
+-- each @Okay@ branch can be of different types.
+--
+-- If both arguments evaluate to @Okay@ the one with the
+-- smaller \"delta\" will be preferred, or--if equal--the
+-- left-hand argument.
+orElse, (|||) :: Predicate a f t -> Predicate a f t' -> Predicate a f (Either t t')
+orElse f g x = f x `cmp` g x
+  where
+    cmp (Okay d y) (Okay w z) = if w < d then Okay w (Right z) else Okay d (Left y)
+    cmp (Okay d y) (Fail   _) = Okay d (Left y)
+    cmp (Fail   _) (Okay d y) = Okay d (Right y)
+    cmp (Fail   _) (Fail   y) = Fail y
+
+(.&.) = and
+(.|.) = or
+(|||) = orElse
+
+-- | Map the result of the given predicate to some other result.
+mapResult :: (Result f t -> Result f' t') -> Predicate a f t -> Predicate a f' t'
+mapResult f p = f . p
+
+-- | Like 'mapResult', but only maps the @Okay@ metadata to another result.
+mapOkay :: (t -> Result f t') -> Predicate a f t -> Predicate a f t'
+mapOkay f p a =
+    case p a of
+        Okay _ x -> f x
+        Fail   x -> Fail x
+
+-- | Like 'mapResult', but only maps the @Fail@ metadata to another result.
+mapFail :: (f -> Result f' t) -> Predicate a f t -> Predicate a f' t
+mapFail f p a =
+    case p a of
+        Fail   x -> f x
+        Okay d x -> Okay d x
+
+-- | A predicate modifier which makes the given predicate optional,
+-- i.e. the @Okay@ metadata type becomes a 'Maybe' and in the failure-case
+-- 'Nothing' is returned.
+opt :: Predicate a f t -> Predicate a f (Maybe t)
+opt = mapResult (result (const $ return Nothing) (\d x -> Okay d (Just x)))
+
+-- | A predicate modifier which returns as @Okay@ metadata the provided default
+-- value if the given predicate fails.
+def :: t -> Predicate a f t -> Predicate a f t
+def t = mapResult (result (const $ return t) Okay)
+
+exec :: Predicate a f t -> a -> (f -> b) -> (t -> b) -> b
+exec p a g f = case p a of
+    Okay _ x -> f x
+    Fail   x -> g x
diff --git a/src/Data/Predicate/Product.hs b/src/Data/Predicate/Product.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Predicate/Product.hs
@@ -0,0 +1,104 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE TypeOperators #-}
+
+module Data.Predicate.Product where
+
+infixr 5 :::
+
+-- | A data-type for combining results of predicate evaluations.
+data a ::: b = a ::: b deriving (Eq, Show)
+
+-- | @flip ($)@ - useful in combination with indexed access, e.g.
+-- @('x' ::: True ::: False)#_2@ yields @True@.
+(#) :: a -> (a -> b) -> b
+(#) = flip ($)
+
+hd :: a ::: b -> a
+hd (a ::: _) = a
+{-# INLINE hd #-}
+
+tl :: a ::: b -> b
+tl (_ ::: b) = b
+{-# INLINE tl #-}
+
+-----------------------------------------------------------------------------
+-- Indexed access (except for last element)
+
+_1 :: a ::: b -> a
+_1 = _1'
+{-# INLINE _1 #-}
+
+_2 :: a ::: b ::: c -> b
+_2 = hd . _2'
+{-# INLINE _2 #-}
+
+_3 :: a ::: b ::: c ::: d -> c
+_3 = hd . _3'
+{-# INLINE _3 #-}
+
+_4 :: a ::: b ::: c ::: d ::: e -> d
+_4 = hd . _4'
+{-# INLINE _4 #-}
+
+_5 :: a ::: b ::: c ::: d ::: e ::: f -> e
+_5 = hd . _5'
+{-# INLINE _5 #-}
+
+_6 :: a ::: b ::: c ::: d ::: e ::: f ::: g -> f
+_6 = hd . _6'
+{-# INLINE _6 #-}
+
+_7 :: a ::: b ::: c ::: d ::: e ::: f ::: g ::: h -> g
+_7 = hd . _7'
+{-# INLINE _7 #-}
+
+_8 :: a ::: b ::: c ::: d ::: e ::: f ::: g ::: h ::: i -> h
+_8 = hd . _8'
+{-# INLINE _8 #-}
+
+_9 :: a ::: b ::: c ::: d ::: e ::: f ::: g ::: h ::: i ::: j -> i
+_9 = hd . _9'
+{-# INLINE _9 #-}
+
+-----------------------------------------------------------------------------
+-- Access last element
+
+_1' :: a ::: b -> a
+_1' = hd
+{-# INLINE _1' #-}
+
+_2' :: a ::: b -> b
+_2' = tl
+{-# INLINE _2' #-}
+
+_3' :: a ::: b ::: c -> c
+_3' = tl . tl
+{-# INLINE _3' #-}
+
+_4' :: a ::: b ::: c ::: d -> d
+_4' = tl . tl . tl
+{-# INLINE _4' #-}
+
+_5' :: a ::: b ::: c ::: d ::: e -> e
+_5' = tl . tl . tl . tl
+{-# INLINE _5' #-}
+
+_6' :: a ::: b ::: c ::: d ::: e ::: f -> f
+_6' = tl . tl . tl . tl . tl
+{-# INLINE _6' #-}
+
+_7' :: a ::: b ::: c ::: d ::: e ::: f ::: g -> g
+_7' = tl . tl . tl . tl . tl . tl
+{-# INLINE _7' #-}
+
+_8' :: a ::: b ::: c ::: d ::: e ::: f ::: g ::: h -> h
+_8' = tl . tl . tl . tl . tl . tl . tl
+{-# INLINE _8' #-}
+
+_9' :: a ::: b ::: c ::: d ::: e ::: f ::: g ::: h ::: i -> i
+_9' = tl . tl . tl . tl . tl . tl . tl . tl
+{-# INLINE _9' #-}
+
diff --git a/src/Data/Predicate/Result.hs b/src/Data/Predicate/Result.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Predicate/Result.hs
@@ -0,0 +1,62 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE TypeOperators #-}
+
+module Data.Predicate.Result where
+
+import Control.Applicative
+import Control.Monad
+
+-- | A 'Bool'-like type where each branch--@Fail@ and @Okay@--carries
+-- some metadata.
+data Result f t
+    = Fail f
+    | Okay !Double t
+    deriving (Eq, Ord, Show)
+
+instance Functor (Result f) where
+    fmap f (Okay d x) = Okay d (f x)
+    fmap _ (Fail   x) = Fail x
+
+instance Applicative (Result f) where
+    pure  = return
+    (<*>) = ap
+
+instance Monad (Result f) where
+    return           = Okay 0
+    (Okay _ x) >>= k = k x
+    (Fail   x) >>= _ = Fail x
+
+result :: (f -> a) -> (Double -> t -> a) -> Result f t -> a
+result f _ (Fail   x) = f x
+result _ g (Okay d x) = g d x
+
+newtype ResultT f m t = ResultT { runResultT :: m (Result f t) }
+
+instance Monad m => Functor (ResultT f m) where
+    fmap f = ResultT . liftM (fmap f) . runResultT
+
+instance Monad m => Applicative (ResultT f m) where
+    pure  = return
+    (<*>) = ap
+
+instance Monad m => Monad (ResultT f m) where
+    return  = ResultT . return . Okay 0
+    m >>= k = ResultT $ runResultT m >>= \a -> case a of
+        Okay _ x -> runResultT (k x)
+        Fail   x -> return (Fail x)
+    fail = ResultT . fail
+
+resultT :: Monad m => (f -> m a) -> (Double -> t -> m a) -> ResultT f m t -> m a
+resultT f g (ResultT m) = m >>= \a -> case a of
+    Fail   x -> f x
+    Okay d x -> g d x
+
+mapResultT :: (m (Result f t) -> n (Result f' t')) -> ResultT f m t -> ResultT f' n t'
+mapResultT f m = ResultT $ f (runResultT m)
+
+hoistResult :: Monad m => Result f t -> ResultT f m t
+hoistResult = ResultT . return
+
diff --git a/src/Network/Wai/Predicate.hs b/src/Network/Wai/Predicate.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate.hs
@@ -0,0 +1,91 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate
+    ( module Data.Predicate
+    , getRequest
+
+    , query
+    , hasQuery
+
+    , header
+    , hasHeader
+
+    , segment
+    , hasSegment
+
+    , cookie
+    , hasCookie
+
+    , accept
+    , contentType
+    , module Network.Wai.Predicate.MediaType
+    , module Network.Wai.Predicate.Error
+    ) where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.From
+import Data.CaseInsensitive (mk)
+import Data.List (find)
+import Data.Monoid
+import Data.Maybe (isJust)
+import Data.Predicate
+import Data.Word
+import Network.HTTP.Types.Status
+import Network.Wai.Predicate.Accept
+import Network.Wai.Predicate.Content
+import Network.Wai.Predicate.Error
+import Network.Wai.Predicate.MediaType
+import Network.Wai.Predicate.Request
+import Network.Wai.Predicate.Utility
+import Network.Wai
+
+getRequest :: (HasRequest r) => Predicate r f Request
+getRequest = return . request
+
+query :: (HasQuery r, FromByteString a) => ByteString -> Predicate r Error a
+query k r = case lookupQuery k r of
+    [] -> Fail (err status400 ("Missing query '" <> k <> "'."))
+    qq -> either (Fail . err status400) return (readValues qq)
+
+hasQuery :: (HasQuery r) => ByteString -> Predicate r Error ()
+hasQuery k r =
+    if null (lookupQuery k r)
+        then Fail (err status400 ("Missing query '" <> k <> "'."))
+        else return ()
+
+header :: (HasHeaders r, FromByteString a) => ByteString -> Predicate r Error a
+header k r = case lookupHeader k r of
+    [] -> Fail (err status400 ("Missing header '" <> k <> "'."))
+    hh -> either (Fail . err status400) return (readValues hh)
+
+hasHeader :: (HasHeaders r) => ByteString -> Predicate r Error ()
+hasHeader k r =
+    if isJust $ find ((mk k ==) . fst) (headers r)
+        then return ()
+        else Fail (err status400 ("Missing header '" <> k <> "'."))
+
+segment :: (HasPath r, FromByteString a) => Word -> Predicate r Error a
+segment i r = case lookupSegment i r of
+    Nothing -> Fail (err status400 "Path segment index out of bounds.")
+    Just  s -> either (Fail . err status400) return (readValues [s])
+
+hasSegment :: (HasPath r) => Word -> Predicate r Error ()
+hasSegment i r =
+    if isJust $ lookupSegment i r
+        then return ()
+        else Fail (err status400 "Path segment index out of bounds.")
+
+cookie :: (HasCookies r, FromByteString a) => ByteString -> Predicate r Error a
+cookie k r = case lookupCookie k r of
+    [] -> Fail (err status400 ("Missing cookie '" <> k <> "'."))
+    cc -> either (Fail . err status400) return (readValues cc)
+
+hasCookie :: (HasCookies r) => ByteString -> Predicate r Error ()
+hasCookie k r =
+    if null (lookupCookie k r)
+        then Fail (err status400 ("Missing cookie '" <> k <> "'."))
+        else return ()
diff --git a/src/Network/Wai/Predicate/Accept.hs b/src/Network/Wai/Predicate/Accept.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Accept.hs
@@ -0,0 +1,46 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE DataKinds         #-}
+{-# LANGUAGE KindSignatures    #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate.Accept
+    ( accept
+    , module Network.Wai.Predicate.MediaType
+    ) where
+
+import Control.Monad
+import Data.ByteString (ByteString)
+import Data.Monoid hiding (All)
+import Data.Maybe
+import Data.Predicate
+import GHC.TypeLits
+import Network.HTTP.Types
+import Network.Wai.Predicate.Error
+import Network.Wai.Predicate.Request
+import Network.Wai.Predicate.MediaType
+
+import qualified Network.Wai.Predicate.Parser.MediaType as M
+
+accept :: (HasHeaders r)
+       => ByteString
+       -> ByteString
+       -> Predicate r Error (Media (t :: Symbol) (s :: Symbol))
+accept t s r =
+    let mtypes = M.readMediaTypes "accept" r in
+    if null mtypes
+        then return (Media t s 1.0 [])
+        else case findMediaType t s mtypes of
+            m:_ -> Okay (1.0 - mediaQuality m) m
+            []  -> Fail (err status406 msg)
+      where
+        msg = "Expected 'Accept: " <> t <> "/" <> s <> "'."
+
+findMediaType :: ByteString -> ByteString -> [M.MediaType] -> [Media t s]
+findMediaType t s = mapMaybe (\m -> do
+    let mt = M.medType m
+        ms = M.medSubtype m
+    guard ((mt == "*" || t == mt) && (ms == "*" || s == ms))
+    return $ Media t s (M.medQuality m) (M.medParams m))
diff --git a/src/Network/Wai/Predicate/Content.hs b/src/Network/Wai/Predicate/Content.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Content.hs
@@ -0,0 +1,49 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE DataKinds         #-}
+{-# LANGUAGE KindSignatures    #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate.Content
+    ( contentType
+    , module Network.Wai.Predicate.MediaType
+    ) where
+
+import Control.Monad
+import Data.ByteString (ByteString)
+import Data.Monoid hiding (All)
+import Data.Predicate
+import GHC.TypeLits
+import Data.Maybe
+import Network.HTTP.Types.Status
+import Network.Wai.Predicate.Error
+import Network.Wai.Predicate.MediaType
+import Network.Wai.Predicate.Request
+
+import qualified Network.Wai.Predicate.Parser.MediaType as M
+
+contentType :: (HasHeaders r)
+            => ByteString
+            -> ByteString
+            -> Predicate r Error (Media (t :: Symbol) (s :: Symbol))
+contentType t s r =
+    let mtypes = M.readMediaTypes "content-type" r in
+    case findContentType t s mtypes of
+        m:_ -> Okay (1.0 - mediaQuality m) m
+        []  -> Fail (err status415 msg)
+  where
+    msg = "Expected 'Content-Type: " <> t <> "/" <> s <> "'."
+
+findContentType :: ByteString -> ByteString -> [M.MediaType] -> [Media t s]
+findContentType t s = mapMaybe (\m -> do
+    let mt = M.medType m
+        ms = M.medSubtype m
+    guard ((t == "*" || t == mt) && (s == "*" || s == ms))
+    return $ Media mt ms (quality t s) (M.medParams m))
+  where
+    quality "*" "*" = 0
+    quality "*"  _  = 0.2
+    quality  _  "*" = 0.5
+    quality  _   _  = 1.0
diff --git a/src/Network/Wai/Predicate/Error.hs b/src/Network/Wai/Predicate/Error.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Error.hs
@@ -0,0 +1,19 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+module Network.Wai.Predicate.Error where
+
+import Data.ByteString (ByteString)
+import Network.HTTP.Types.Status
+
+-- | The error type used as meta-data for @F@ in all WAI predicates.
+data Error = Error
+    { status  :: !Status          -- ^ HTTP status code
+    , message :: Maybe ByteString -- ^ optional status message
+    } deriving (Eq, Show)
+
+-- | Convenience function to construct 'Error' values from
+-- status code and body message.
+err :: Status -> ByteString -> Error
+err s = Error s . Just
diff --git a/src/Network/Wai/Predicate/MediaType.hs b/src/Network/Wai/Predicate/MediaType.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/MediaType.hs
@@ -0,0 +1,31 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE DataKinds      #-}
+{-# LANGUAGE KindSignatures #-}
+
+module Network.Wai.Predicate.MediaType where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.Char8 (pack)
+import GHC.TypeLits
+
+data Media (t :: Symbol) (s :: Symbol) = Media
+    { rawType      :: !ByteString
+    , rawSubTypes  :: !ByteString
+    , mediaQuality :: !Double
+    , mediaParams  :: ![(ByteString, ByteString)]
+    } deriving (Eq, Show)
+
+mediaType :: SingI t => Media t s -> ByteString
+mediaType m = withSing (f m)
+  where
+    f :: Media t s -> Sing t -> ByteString
+    f _ t = pack (fromSing t)
+
+mediaSubType :: SingI s => Media t s -> ByteString
+mediaSubType m = withSing (f m)
+  where
+    f :: Media t s -> Sing s -> ByteString
+    f _ s = pack (fromSing s)
diff --git a/src/Network/Wai/Predicate/Parser/MediaType.hs b/src/Network/Wai/Predicate/Parser/MediaType.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Parser/MediaType.hs
@@ -0,0 +1,76 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate.Parser.MediaType
+    ( MediaType (..)
+    , readMediaTypes
+    ) where
+
+import Control.Applicative
+import Data.Attoparsec.Char8
+import Data.ByteString (ByteString)
+import Data.List (sortBy)
+import Network.Wai.Predicate.Request
+
+import qualified Data.ByteString.Char8 as C
+
+data MediaType = MediaType
+    { medType    :: !ByteString
+    , medSubtype :: !ByteString
+    , medQuality :: !Double
+    , medParams  :: ![(ByteString, ByteString)]
+    } deriving (Eq, Show)
+
+readMediaTypes :: (HasHeaders r) => ByteString -> r -> [MediaType]
+readMediaTypes k r =
+    sortBy q . concatMap parseMediaTypes $ lookupHeader k r
+  where
+    q a b = medQuality b `compare` medQuality a
+
+parseMediaTypes :: ByteString -> [MediaType]
+parseMediaTypes = either (const []) id . parseOnly mediaTypes
+
+mediaTypes :: Parser [MediaType]
+mediaTypes = mediaType `sepBy` char ','
+
+mediaType :: Parser MediaType
+mediaType =
+    toMediaType <$> trim typ <*> (char '/' *> trim subtyp) <*> params
+  where
+    toMediaType t s p =
+        case lookup "q" p >>= toDouble of
+            Just q  -> MediaType t s q (filter ((/= "q") . fst) p)
+            Nothing -> MediaType t s 1.0 p
+
+params :: Parser [(ByteString, ByteString)]
+params = (trim (char ';') *> (element `sepBy` trim (char ';'))) <|> return []
+  where
+    element = (,) <$> trim key <*> (char '=' *> trim val)
+
+typ, subtyp, key, val :: Parser ByteString
+typ    = takeTill (oneof "/ ")
+subtyp = takeTill (oneof ",; ")
+
+key = do
+    c <- peekChar
+    if c == Just ',' then fail "comma" else takeTill (oneof "= ")
+
+val = takeTill (oneof ",; ")
+
+toDouble :: ByteString -> Maybe Double
+toDouble bs = toMaybe (parseOnly double bs)
+  where
+    toMaybe (Right x) = Just x
+    toMaybe (Left  _) = Nothing
+
+spaces :: Parser ()
+spaces = skipWhile (== ' ')
+
+trim :: Parser a -> Parser a
+trim p = spaces *> p <* spaces
+
+oneof :: ByteString -> Char -> Bool
+oneof s c = C.any (== c) s
diff --git a/src/Network/Wai/Predicate/Request.hs b/src/Network/Wai/Predicate/Request.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Request.hs
@@ -0,0 +1,119 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate.Request
+    ( Req
+    , HasMethod  (..)
+    , HasHeaders (..)
+    , HasCookies (..)
+    , HasQuery   (..)
+    , HasPath    (..)
+    , HasRequest (..)
+
+    , fromRequest
+    , lookupHeader
+    , lookupQuery
+    , lookupCookie
+    , lookupSegment
+    ) where
+
+import Data.ByteString (ByteString)
+import Data.CaseInsensitive (mk)
+import Data.Maybe (mapMaybe)
+import Data.Vector (Vector, (!?))
+import Data.Word
+import Network.HTTP.Types
+import Network.Wai (Request)
+import Web.Cookie
+
+import qualified Data.ByteString as B
+import qualified Network.Wai     as Wai
+import qualified Data.Vector     as Vec
+
+class HasRequest a where
+    request :: a -> Wai.Request
+
+class HasMethod a where
+    method :: a -> Method
+
+class HasHeaders a where
+    headers :: a -> RequestHeaders
+
+class HasCookies a where
+    cookies :: a -> Cookies
+
+class HasQuery a where
+    queryItems :: a -> Query
+
+class HasPath a where
+    segments :: a -> Vector ByteString
+
+data Req = Req
+    { _request  :: Request
+    , _cookies  :: Cookies
+    , _segments :: Vector ByteString
+    }
+
+instance HasRequest Req where
+    request = _request
+
+instance HasMethod Req where
+    method = Wai.requestMethod . request
+
+instance HasMethod Wai.Request where
+    method = Wai.requestMethod
+
+instance HasHeaders Req where
+    headers = Wai.requestHeaders . request
+
+instance HasHeaders Wai.Request where
+    headers = Wai.requestHeaders
+
+instance HasQuery Req where
+    queryItems = Wai.queryString . request
+
+instance HasQuery Wai.Request where
+    queryItems = Wai.queryString
+
+instance HasCookies Req where
+    cookies = _cookies
+
+instance HasPath Req where
+    segments = _segments
+
+fromRequest :: Request -> Req
+fromRequest rq =
+    Req rq (concatMap parseCookies (getHeaders "Cookie" rq))
+           (Vec.fromList . splitSegments . Wai.rawPathInfo $ rq)
+
+lookupHeader :: HasHeaders r => ByteString -> r -> [ByteString]
+lookupHeader name = getHeaders name
+
+lookupSegment :: HasPath r => Word -> r -> Maybe ByteString
+lookupSegment i r = segments r !? fromIntegral i
+
+lookupCookie :: HasCookies r => ByteString -> r -> [ByteString]
+lookupCookie name = map snd . filter ((name ==) . fst) . cookies
+
+lookupQuery :: HasQuery r => ByteString -> r -> [ByteString]
+lookupQuery name = mapMaybe snd . filter ((name ==) . fst) . queryItems
+
+getHeaders :: HasHeaders r => ByteString -> r -> [ByteString]
+getHeaders name = map snd . filter ((mk name ==) . fst) . headers
+
+-----------------------------------------------------------------------------
+-- Internal
+
+splitSegments :: ByteString -> [ByteString]
+splitSegments a
+    | B.null a  = []
+    | "/" == a  = []
+    | otherwise = if B.head a == slash then go (B.tail a) else go a
+  where
+    go b =
+        let (x, y) = B.breakByte slash b
+        in urlDecode False x : if B.null y then [] else go (B.tail y)
+    slash = 47
diff --git a/src/Network/Wai/Predicate/Utility.hs b/src/Network/Wai/Predicate/Utility.hs
new file mode 100644
--- /dev/null
+++ b/src/Network/Wai/Predicate/Utility.hs
@@ -0,0 +1,20 @@
+-- This Source Code Form is subject to the terms of the Mozilla Public
+-- License, v. 2.0. If a copy of the MPL was not distributed with this
+-- file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Network.Wai.Predicate.Utility (readValues) where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.From
+import Data.List (foldl')
+import Data.String (fromString)
+
+readValues :: FromByteString a => [ByteString] -> Either ByteString a
+readValues = foldl' res (Left "no parse") . map (runParser parser)
+  where
+    res (Left  _) (Right x) = Right x
+    res (Right x) _         = Right x
+    res _         (Left  x) = Left (fromString x)
+
diff --git a/test/TestSuite.hs b/test/TestSuite.hs
new file mode 100644
--- /dev/null
+++ b/test/TestSuite.hs
@@ -0,0 +1,11 @@
+module Main where
+
+import Test.Tasty
+import qualified Tests.Data.Predicate as Predicate
+import qualified Tests.Wai.Predicate  as WaiPredicate
+
+main :: IO ()
+main = defaultMain $ testGroup "Tests"
+    [ Predicate.tests
+    , WaiPredicate.tests
+    ]
diff --git a/test/Tests/Data/Predicate.hs b/test/Tests/Data/Predicate.hs
new file mode 100644
--- /dev/null
+++ b/test/Tests/Data/Predicate.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE FlexibleInstances    #-}
+{-# LANGUAGE OverlappingInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Tests.Data.Predicate (tests) where
+
+import Control.Applicative hiding (Const, empty)
+import Data.Predicate
+import Test.QuickCheck hiding (Result, (.&.))
+import Test.Tasty
+import Test.Tasty.QuickCheck hiding ((.&.))
+
+tests :: TestTree
+tests = testGroup "Data.Predicate"
+    [ testProperty ".&." testAnd
+    , testProperty "|||" testOr
+    , testProperty ".|." testOr'
+    ]
+
+testAnd :: Predicate () Int Char -> Predicate () Int Char -> Bool
+testAnd a b = case (a (), b ()) of
+    (Okay d x, Okay w y) -> (a .&. b) () == Okay (d + w) (x ::: y)
+    (Okay _ _, Fail   y) -> (a .&. b) () == Fail y
+    (Fail   x, Okay _ _) -> (a .&. b) () == Fail x
+    (Fail   x, Fail   _) -> (a .&. b) () == Fail x
+
+testOr :: Predicate () Int Char -> Predicate () Int Char -> Bool
+testOr a b = case (a (), b ()) of
+    (Okay d x, Okay e y) -> (a ||| b) () == if d <= e then Okay d (Left x) else Okay e (Right y)
+    (Okay d x, Fail   _) -> (a ||| b) () == Okay d (Left x)
+    (Fail   _, Okay d y) -> (a ||| b) () == Okay d (Right y)
+    (Fail   _, Fail   y) -> (a ||| b) () == Fail y
+
+testOr' :: Predicate () Int Char -> Predicate () Int Char -> Bool
+testOr' a b = case (a (), b ()) of
+    (Okay d x, Okay e y) -> (a .|. b) () == if d <= e then Okay d x else Okay e y
+    (Okay d x, Fail   _) -> (a .|. b) () == Okay d x
+    (Fail   _, Okay d y) -> (a .|. b) () == Okay d y
+    (Fail   _, Fail   y) -> (a .|. b) () == Fail y
+
+instance Arbitrary (Result Int Char) where
+    arbitrary =
+        oneof [ Okay <$> (arbitrary :: Gen Double) <*> (arbitrary :: Gen Char)
+              , Fail <$> (arbitrary :: Gen Int)
+              ]
+
+instance Arbitrary (Predicate () Int Char) where
+    arbitrary = (\r -> const r) <$> (arbitrary :: Gen (Result Int Char))
diff --git a/test/Tests/Wai/Predicate.hs b/test/Tests/Wai/Predicate.hs
new file mode 100644
--- /dev/null
+++ b/test/Tests/Wai/Predicate.hs
@@ -0,0 +1,84 @@
+{-# LANGUAGE DataKinds         #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Tests.Wai.Predicate (tests) where
+
+import Data.ByteString (ByteString)
+import Network.HTTP.Types.Status
+import Network.Wai.Predicate
+import Network.Wai.Predicate.Request
+import Test.Tasty
+import Test.Tasty.HUnit
+import Tests.Wai.Util
+
+tests :: TestTree
+tests = testGroup "Wai.Predicate"
+    [ testCase "Accept application/json" testAcceptJson
+    , testCase "Accept application/thrift " testAcceptThrift
+    , testCase "Accept application/*" testAcceptAll
+    , testCase "Content-Type text/plain" testContentTypePlain
+    , testCase "Content-Type text/*" testContentTypeAll
+    , testCase "Query" testQuery
+    , testCase "QueryOpt" testQueryOpt
+    , testCase "exec" testExec
+    ]
+
+testAcceptJson :: IO ()
+testAcceptJson = do
+    let rq0 = fromRequest . json $ defRequest "/"
+    Okay 0 (Media "application" "json" 1.0 []) @=? (accept "application" "json") rq0
+
+    let rq1 = fromRequest . withHeader "Accept" "foo/bar" $ defRequest "/"
+    Fail (err status406 ("Expected 'Accept: application/json'.")) @=? (accept "application" "json") rq1
+
+testAcceptThrift :: IO ()
+testAcceptThrift = do
+    let rq0 = fromRequest . withHeader "Accept" "application/x-thrift" $ defRequest "/"
+    Okay 0 (Media "application" "x-thrift" 1.0 []) @=? (accept "application" "x-thrift") rq0
+
+    let rq1 = fromRequest . json $ defRequest "/"
+    Fail (err status406 ("Expected 'Accept: application/x-thrift'.")) @=? (accept "application" "x-thrift") rq1
+
+testAcceptAll :: IO ()
+testAcceptAll = do
+    let rq0 = fromRequest . withHeader "Accept" "application/*" $ defRequest "/"
+    Okay 0 (Media "application" "*"    1.0 []) @=? (accept "application" "*") rq0
+    Okay 0 (Media "application" "json" 1.0 []) @=? (accept "application" "json") rq0
+
+testContentTypePlain :: IO ()
+testContentTypePlain = do
+    let rq0 = fromRequest . withHeader "Content-Type" "text/plain" $ defRequest "/"
+    Okay 0 (Media "text" "plain" 1.0 []) @=? (contentType "text" "plain") rq0
+
+    let rq1 = fromRequest . withHeader "Content-Type" "text/html" $ defRequest "/"
+    Fail (err status415 ("Expected 'Content-Type: text/plain'.")) @=? (contentType "text" "plain") rq1
+
+testContentTypeAll :: IO ()
+testContentTypeAll = do
+    let rq0 = fromRequest . withHeader "Content-Type" "text/plain" $ defRequest "/"
+    Okay 0.5 (Media "text" "plain" 0.5 []) @=? (contentType "text" "*") rq0
+
+testQuery :: IO ()
+testQuery = do
+    let rq0 = fromRequest . withQuery "x" "y" . withQuery "x" "z" $ defRequest "/"
+    Okay 0 ("y" :: ByteString) @=? (query "x") rq0
+
+    let rq1 = fromRequest $ defRequest "/"
+    Fail (err status400 ("Missing query 'x'.")) @=? (query "x" :: Predicate Req Error ByteString) rq1
+
+testQueryOpt :: IO ()
+testQueryOpt = do
+    let rq0 = fromRequest . withQuery "x" "y" . withQuery "x" "z" $ defRequest "/"
+    Okay 0 (Just ("y" :: ByteString)) @=? (opt (query "x")) rq0
+
+    let rq1 = fromRequest $ defRequest "/"
+    Okay 0 Nothing @=? (opt (query "x" :: Predicate Req Error ByteString)) rq1
+
+testExec :: IO ()
+testExec = do
+    let unit = const $ return ()
+    let rq = fromRequest . withQuery "x" "42" . withHeader "a" "b" $ defRequest "/"
+    exec (query "x" .&. header "a") rq unit $ \args -> do
+        args#_1  @=? (42  :: Int)
+        args#_2' @=? ("b" :: ByteString)
+
diff --git a/test/Tests/Wai/Util.hs b/test/Tests/Wai/Util.hs
new file mode 100644
--- /dev/null
+++ b/test/Tests/Wai/Util.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Tests.Wai.Util where
+
+import Data.ByteString (ByteString)
+import Data.CaseInsensitive (CI)
+import Network.Wai
+import Network.Wai.Internal
+import Network.HTTP.Types
+
+import qualified Data.ByteString.Lazy     as Lazy
+import qualified Blaze.ByteString.Builder as Builder
+
+defRequest :: ByteString -> Request
+defRequest p = defaultRequest { rawPathInfo = p }
+
+withHeader :: CI ByteString -> ByteString -> Request -> Request
+withHeader k v r = r { requestHeaders = (k, v) : requestHeaders r }
+
+withQuery :: ByteString -> ByteString -> Request -> Request
+withQuery k v r = r { queryString = (k, Just v) : queryString r }
+
+json :: Request -> Request
+json = withHeader "Accept" "application/json"
+
+responseBody :: Response -> Lazy.ByteString
+responseBody (ResponseBuilder _ _ b) = Builder.toLazyByteString b
+responseBody _                       = ""
+
+writeText :: Lazy.ByteString -> IO Response
+writeText = return . responseLBS status200 []
diff --git a/wai-predicates.cabal b/wai-predicates.cabal
new file mode 100644
--- /dev/null
+++ b/wai-predicates.cabal
@@ -0,0 +1,85 @@
+name:                wai-predicates
+version:             0.1
+synopsis:            WAI request predicates
+license:             OtherLicense
+license-file:        LICENSE
+author:              Toralf Wittner
+maintainer:          Toralf Wittner <tw@dtex.org>
+copyright:           (c) 2014 Toralf Wittner
+stability:           experimental
+category:            Web
+build-type:          Simple
+cabal-version:       >= 1.10
+
+extra-source-files:
+    README.md
+
+description:
+    Evaluate predicate functions against WAI requests and receive
+    metadata in addition to a success/failure indicator.
+    Predicates can be combined using logical connectives and the
+    metadata are passed on accordingly.
+
+source-repository head
+    type:             git
+    location:         git://github.com/twittner/wai-predicates.git
+
+library
+    default-language: Haskell2010
+    hs-source-dirs:   src
+    ghc-options:      -Wall -O2 -fwarn-tabs -funbox-strict-fields
+    ghc-prof-options: -prof -auto-all
+
+    exposed-modules:
+        Data.Predicate
+        Network.Wai.Predicate
+        Network.Wai.Predicate.Error
+        Network.Wai.Predicate.MediaType
+        Network.Wai.Predicate.Request
+        Network.Wai.Predicate.Utility
+
+    other-modules:
+        Data.Predicate.Product
+        Data.Predicate.Result
+        Network.Wai.Predicate.Accept
+        Network.Wai.Predicate.Content
+        Network.Wai.Predicate.Parser.MediaType
+
+    build-depends:
+        attoparsec       >= 0.10  && < 0.12
+      , base             == 4.*
+      , bytestring       >= 0.9   && < 0.11
+      , bytestring-from  == 0.2.*
+      , cookie           == 0.4.*
+      , case-insensitive == 1.1.*
+      , http-types       == 0.8.*
+      , vector           == 0.10.*
+      , wai              == 2.0.*
+
+test-suite wai-predicate-tests
+    type:             exitcode-stdio-1.0
+    default-language: Haskell2010
+    hs-source-dirs:   test
+    main-is:          TestSuite.hs
+    ghc-options:      -Wall -O2 -fwarn-tabs
+    ghc-prof-options: -prof -auto-all
+
+    other-modules:
+        Tests.Data.Predicate
+        Tests.Wai.Predicate
+        Tests.Wai.Util
+
+    build-depends:
+        base             == 4.*
+      , blaze-builder    == 0.3.*
+      , bytestring       >= 0.9 && < 0.11
+      , case-insensitive == 1.1.*
+      , http-types       == 0.8.*
+      , HUnit            >= 1.2
+      , QuickCheck       >= 2.3
+      , tasty            >= 0.3
+      , tasty-hunit      >= 0.2
+      , tasty-quickcheck >= 0.3
+      , wai
+      , wai-predicates
+