placeholders
============
While working on some Haskell code, it is often useful to develop
incrementally by inserting `undefined` as a placeholder for missing code.
This approach has a couple of drawbacks.
* If you have several occurrences of `undefined` in your code, it can be hard
to track down the one reponsible for the error at run-time.
* It is too easy to forget to replace `undefined` with the proper code, which
might cause unexpected errors.
This library provides placeholders that produce better messages when
evaluated at run-time and also generate compile-time warnings so that they do
not get forgotten so easily.
example
=======
{-# LANGUAGE TemplateHaskell #-}
import Development.Placeholders
theUltimateAnswer :: Int
theUltimateAnswer = $notImplemented
main = do
putStrLn "The ultimate answer:"
print theUltimateAnswer
This will compile with a warning about the unimplemented function:
$ ghc --make Simple.hs
...
Simple.hs:6:21: Unimplemented feature
...
At runtime, an exception will be thrown when the placeholder is evaluated,
indicating the location of the placeholder.
$ ./Simple
The ultimate answer:
Simple: PlaceholderExcption "Unimplemented feature at Simple.hs:6:21"
If compiled with the GHC flag `-Werror`, the warning will get turned into
an error and compilation will fail. `-Werror` can therefore be used to
verify that you haven't left any unintended placeholders behind.