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Today's Topics:
1. wierd quickcheck outcome (Roelof Wobben)
2. Re: wierd quickcheck outcome (Frerich Raabe)
3. Re: wierd quickcheck outcome (Kim-Ee Yeoh)
----------------------------------------------------------------------
Message: 1
Date: Thu, 10 Sep 2015 09:23:29 +0200
From: Roelof Wobben <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] wierd quickcheck outcome
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Hello,
I have this function :
fourDifferent:: Integer -> Integer -> Integer -> Integer -> Bool
fourDifferent a b c d = ( a == b ) && ( a == c ) && (a == d)
which I wants to test with this function :
prop_fourDifferent :: Integer -> Integer -> Integer -> Integer -> Bool
prop_fourDifferent a b c d = fourDifferent a b c d == ( a == b ) && ( a
== c ) && (a == d)
so I do quickCheck propFourDifferent and see this outcome :
*Solution> quickCheck prop_fourDifferent
*** Failed! Falsifiable (after 2 tests and 2 shrinks):
0
0
0
1
*Solution> fourDifferent 0 0 0 1
False
*Solution> let a = 0
*Solution> let b = 0
*Solution> let c = 0
*Solution> let d = 1
*Solution> (a == b) && ( a == c) && ( a == d ) False
*Solution>
So why is it failing. both gives false ,
Roelof
------------------------------
Message: 2
Date: Thu, 10 Sep 2015 09:54:37 +0200
From: Frerich Raabe <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] wierd quickcheck outcome
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII; format=flowed
On 2015-09-10 09:23, Roelof Wobben wrote:
> which I wants to test with this function :
>
> prop_fourDifferent :: Integer -> Integer -> Integer -> Integer -> Bool
> prop_fourDifferent a b c d = fourDifferent a b c d == ( a == b ) && ( a == c
> ) && (a == d)
The problem is that (==) has a higher precedence (4) than (&&) (which has
precedence 3). So your definition is equivalent to
prop_fourDifferent a b c d = (fourDifferent a b c d == ( a == b )) && ( a
== c ) && (a == d)
You need some extra parentheses there, try
prop_fourDifferent a b c d = fourDifferent a b c d == (( a == b ) && ( a ==
c ) && (a == d))
--
Frerich Raabe - [email protected]
www.froglogic.com - Multi-Platform GUI Testing
------------------------------
Message: 3
Date: Thu, 10 Sep 2015 16:25:03 +0700
From: Kim-Ee Yeoh <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] wierd quickcheck outcome
Message-ID:
<CAPY+ZdSdvKZRv8q+NC2Gzzs2mVkSp38O22UHZ3rYpf=g3gr...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi Roelof,
> False == True && False
False
> False == (True && False)
True
> :info (==)
class Eq a where
(==) :: a -> a -> Bool
infix 4 ==
> :info (&&)
(&&) :: Bool -> Bool -> Bool
infixr 3 &&
So (==) at level 4 binds tighter than (&&) at level 3.
See: https://www.haskell.org/onlinereport/decls.html#fixity
-- Kim-Ee
On Thu, Sep 10, 2015 at 2:23 PM, Roelof Wobben <[email protected]> wrote:
> Hello,
>
> I have this function :
>
> fourDifferent:: Integer -> Integer -> Integer -> Integer -> Bool
> fourDifferent a b c d = ( a == b ) && ( a == c ) && (a == d)
>
> which I wants to test with this function :
>
> prop_fourDifferent :: Integer -> Integer -> Integer -> Integer -> Bool
> prop_fourDifferent a b c d = fourDifferent a b c d == ( a == b ) && ( a ==
> c ) && (a == d)
>
> so I do quickCheck propFourDifferent and see this outcome :
>
> *Solution> quickCheck prop_fourDifferent
> *** Failed! Falsifiable (after 2 tests and 2 shrinks):
> 0
> 0
> 0
> 1
>
> *Solution> fourDifferent 0 0 0 1
> False
> *Solution> let a = 0
> *Solution> let b = 0
> *Solution> let c = 0
> *Solution> let d = 1
> *Solution> (a == b) && ( a == c) && ( a == d ) False
> *Solution>
>
>
> So why is it failing. both gives false ,
>
> Roelof
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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