Thanks for this respons, Rubén. I might not have explained what I am
looking for very well.
I already have
instance Arbitrary Foo
That is not the problem. The problem is, that when a counterexample is
found, it is dumped to the output with the `show` function. I would like to
be able to use another function for that, say show'. In order to do so, I
need to obtain the counterexample itself in some way, so I can use it to
generate a useful message after the tests are done.
Op vr 11 jun. 2021 om 23:31 schreef Ruben Astudillo
Hello Han
On 11-06-21 17:16, Han Joosten wrote:
[..] *parseFoo :: Text -> Guarded Foo* *prettyFoo :: Foo -> Text*
The idea is that for all foo :: Foo, the following holds: *parseFoo . prettyFoo $ foo* should be equal to *Checked foo []*
Now, if there is a counterexample, I would like to see prettyFoo foo as output, folowed by the show of the Errors part.
It seems you know what property should hold for `parseFoo` and `prettyFoo`. Per the QuickCheck manual [1] this could be written as
import Test.QuickCheck
propOnAllFooText :: Property propOnAllFooText = forAll (arbitrary :: Gen Foo) $ \exFoo -> parseFoo (prettyFoo exFoo) == Checked exFoo []
What you are missing is a way to generate the test cases (the `arbitrary' generator above). You need a way to declare this instance
instance Arbitrary Foo where -- arbitrary :: Gen Foo arbitrary = <something>
You can see example on how to define it on the manual [1]. Good luck.
[1]: http://www.cse.chalmers.se/~rjmh/QuickCheck/manual.html
-- -- Rubén -- pgp: 4EE9 28F7 932E F4AD