Dumps the names and values of expressions to ease debugging.

Can be used with Debug.Trace, Test.QuickCheck, or just plain old System.IO's "putStrLn".

See README.md and FEATURES.md for further details.

Example usage:

{-# LANGUAGE QuasiQuotes #-}

import Debug.Dump

main = print [d|a, a+1, map (+a) [1..3]|]
  where a = 2

which prints:

(a) = 2   (a+1) = 3       (map (+a) [1..3]) = [3,4,5]

by turnint this String

"a, a+1, map (+a) [1..3]"

into this expression

( "(a) = " ++ show (a)            ++ "\t  " ++
  "(a+1) = " ++ show (a + 1)      ++ "\t  " ++
  "(map (+a) [1..3]) = " ++ show (map (+ a) [1 .. 3])
)

QuickCheck

If you have any intermediate computation within a QuickCheck property, it can be useful to print a counterexample simply in case of failure

{-# LANGUAGE QuasiQuotes #-}

import Debug.Dump
import Test.QuickCheck

($>) = flip ($); infixl 0 $>

prop :: Float -> Property
prop n = n == 1 / (1 / n)
  $> counterexample [d|n, 1/n, 1/(1/n)|]

main = quickCheck prop

Which, when executed, will print something like this:

*** Failed! Falsifiable (after 15 tests and 133 shrinks):
1.7051912e-38
(n) = 1.7051912e-38   (1/n) = 5.864445e37   (1/(1/n)) = 1.7051913e-38

Isn't it nice to see the intermediate computations as well?

See also: list of features

Concieved at this StackOverflow question.