Example usage:

{-# LANGUAGE QuasiQuotes #-}
importDebug.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 #-}
importDebug.DumpimportTest.QuickCheck($>)=flip($); infixl0$>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.