Initial commit

.gitignore

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+dist

LICENSE

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+Copyright (c) 2011, Andreas Hammar
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Andreas Hammar nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Setup.hs

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+import Distribution.Simple
+main = defaultMain

placeholders.cabal

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+Name:                placeholders
+Version:             0.1
+Synopsis:            Placeholders for use under development
+Description:         TODO: Add a description
+Homepage:            http://github.com/ahammar/placeholders
+License:             BSD3
+License-file:        LICENSE
+Author:              Andreas Hammar
+Maintainer:          Andreas Hammar <ahammar@gmail.com>
+Copyright:           (c) 2011 Andreas Hammar
+Category:            Development
+Build-type:          Simple
+Cabal-version:       >=1.6
+
+Source-repository head
+  Type:        git
+  Location:    git://github.com/ahammar/placeholders.git
+
+Library
+  Exposed-modules:     Development.Placeholders
+
+  Build-depends:       base >= 4 && < 5,
+                       template-haskell
+
+  Hs-source-dirs:      src
+

src/Development/Placeholders.hs

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+{-# LANGUAGE TemplateHaskell, DeriveDataTypeable #-}
+
+module Development.Placeholders (
+    PlaceholderException(..),
+    placeholder,
+    placeholderNoWarning,
+    notImplemented,
+    todo
+) where
+
+import Control.Exception (Exception, throw)
+import Data.Typeable (Typeable)
+import Language.Haskell.TH (Q, Exp, Loc(..), litE, stringL, location, report)
+
+-- | Thrown when attempting to evaluate a placeholder at runtime.
+data PlaceholderException = PlaceholderException String
+    deriving (Show, Typeable)
+
+instance Exception PlaceholderException
+
+-- | Shorthand for @placeholder "Unimplemented feature"@
+notImplemented :: Q Exp
+notImplemented = placeholder "Unimplemented feature"
+
+-- | Shorthand for @placeholder ("TODO: " ++ msg)@
+todo :: String -> Q Exp
+todo msg = placeholder $ "TODO: " ++ msg
+
+-- | Generates an expression of any type that, if evaluated at runtime will throw
+-- a 'PlaceholderException'. It is therefore similar to 'undefined' or 'error',
+-- except that this clearly communicates that this is temporary, and the source
+-- location is automatically included. Also, a warning is generated at compile time
+-- so you won't forget to replace placeholders before shipping.
+placeholder :: String -> Q Exp
+placeholder msg = do
+    emitWarning msg
+    placeholderNoWarning msg
+
+-- | Similar to 'placeholder', but does not generate a compiler warning. Use
+-- with care!
+placeholderNoWarning :: String -> Q Exp
+placeholderNoWarning msg = do
+    runtimeMsg <- formatMessage msg `fmap` location
+    [| throw $ PlaceholderException $(litE $ stringL runtimeMsg) |]
+
+emitWarning :: String -> Q ()
+emitWarning msg = report False $ msg
+
+formatMessage :: String -> Loc -> String
+formatMessage msg loc = msg ++ " at " ++ formatLoc loc
+
+formatLoc :: Loc -> String
+formatLoc loc = let file = loc_filename loc
+                    (line, col) = loc_start loc
+                in concat [file, ":", show line, ":", show col]
+