[Haskell-beginners] Quickcheck: pushing element onto stack increases stack size

PATRICK BROWNE patrick.browne at dit.ie
Thu May 11 21:55:55 UTC 2017


David,
Thanks for the help.
Much appreciated,
Pat

On 11 May 2017 at 21:00, David McBride <toad3k at gmail.com> wrote:

> First you need a way to generate an arbitrary stack.  Here's a simple
> method that just gives you a 50% chance at each level of generating an
> extra layer.
>
> instance Arbitrary a => Arbitrary (Stack a) where
>   arbitrary = oneof [return Empty, Push <$> arbitrary <*> arbitrary ]
>
> prop_size_succeeds x s = size (Push x s) > size s
> prop_size_fails x s = size s > size Empty
>
> >quickCheck prop_size_fails
> *** Failed! Falsifiable (after 6 tests):
> ()
> Empty
>
>
> On Thu, May 11, 2017 at 3:38 PM, PATRICK BROWNE <patrick.browne at dit.ie>
> wrote:
> > Hi,
> > I am trying to use Quickcheck to check that pushing an element increases
> the
> > size of a stack.
> > Something like:
> > prop_size2 x s = (size (Push x s)) > (size s)
> >
> > Is this possible? Below is my effort using an empty stack.
> > Thanks in advance,
> > Pat
> >
> >
> > module Stack (empty, push, pop, top, isEmpty) where
> > import Test.QuickCheck
> >
> > data Stack a = Empty | Push a (Stack a) deriving  Show
> >
> > empty :: Stack a
> > empty = Empty
> >
> > push :: a -> Stack a -> Stack a
> > push x ss = Push x ss
> >
> > pop :: Stack a -> Stack a
> > pop Empty = error "pop emptyStack"
> > pop (Push x ss) = ss
> >
> > top :: Stack a -> a
> > top Empty = error "top emptyStack"
> > top (Push x ss) = x
> >
> > isEmpty :: Stack a -> Bool
> > isEmpty Empty = True
> > isEmpty (Push x ss) = False
> >
> >
> > size :: (Stack a) -> Int
> > size Empty = 0
> > size (Push x ss) = succ (size ss)
> >
> >
> > prop_size x  = (size (Push x Empty)) > (size Empty)
> >
> > This email originated from DIT. If you received this email in error,
> please
> > delete it from your system. Please note that if you are not the named
> > addressee, disclosing, copying, distributing or taking any action based
> on
> > the contents of this email or attachments is prohibited. www.dit.ie
> >
> > Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí
> > earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an
> > seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon
> > dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa
> ríomhphost
> > nó sna hiatáin seo. www.dit.ie
> >
> > Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to
> > Grangegorman
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
>

-- 


This email originated from DIT. If you received this email in error, please 
delete it from your system. Please note that if you are not the named 
addressee, disclosing, copying, distributing or taking any action based on 
the contents of this email or attachments is prohibited. www.dit.ie

Is ó ITBÁC a tháinig an ríomhphost seo. Má fuair tú an ríomhphost seo trí 
earráid, scrios de do chóras é le do thoil. Tabhair ar aird, mura tú an 
seolaí ainmnithe, go bhfuil dianchosc ar aon nochtadh, aon chóipeáil, aon 
dáileadh nó ar aon ghníomh a dhéanfar bunaithe ar an ábhar atá sa 
ríomhphost nó sna hiatáin seo. www.dit.ie

Tá ITBÁC ag aistriú go Gráinseach Ghormáin – DIT is on the move to 
Grangegorman <http://www.dit.ie/grangegorman>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/beginners/attachments/20170511/71506976/attachment.html>


More information about the Beginners mailing list