placeholders-0.1: Placeholders for use while developing Haskell code

Safe HaskellNone
LanguageHaskell98

Development.Placeholders

Contents

Description

This module defines placeholders that you can use while coding to allow incomplete code to compile. They work just like undefined, but with improved error messages and compile-time warnings.

Synopsis

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:

@

Placeholders

notImplemented :: Q Exp #

Indicates that this piece of code has not yet been implemented.

$notImplemented = $(placeholder "Unimplemented feature")

todo :: String -> Q Exp #

Indicates unimplemented code or a known bug with a custom message.

$(todo msg) = $(placeholder ("TODO: " ++ msg))

placeholder :: String -> Q Exp #

Generates an expression of any type that, if evaluated at runtime will throw a PlaceholderException. It is therefore similar to error, except that the source location is automatically included. Also, a warning is generated at compile time so you won't forget to replace placeholders before packaging your code.

placeholderNoWarning :: String -> Q Exp #

Similar to placeholder, but does not generate a compiler warning. Use with care!

Exceptions

data PlaceholderException #

Thrown when attempting to evaluate a placeholder at runtime.

Constructors

PlaceholderException String 

Instances