Mukesh,

You need to write a generator function for the type (IntMap Index) which

keeps track of the n parameter that you're using in arbIndex.

You can't rely on the Arbitrary instance for (IntMap a) because it

doesn't have access to the n parameter that you are so controlling

in arbIndex.

(Actually, you could use the "size" number that QuickCheck keeps

behind the scenes, using the functions "sized" and "resize", but that

would have the consequence of affecting all other arbitrary values

generated as part of that recursion--including the floats and ints and

so on, which may or may not be what you want.)

Also, since your trees are unranked, rather than binary as in the paper

example, take care with the factor of 2 that you're using to resize the

generated subtrees. You might find that the resulting trees are still

much bigger than you want, or have different statistical properties.

Hope that helps--

Ezra

On Friday, September 23, 2011 4:22 AM, "mukesh tiwari" <mukeshtiwari.iiitm@gmail.com> wrote:

Hello all
I have a   data type
data Index = Index {indexSize::Float, indexIds::[Int], indexDown::(IntMap.IntMap Index)}
| IndexLeaf {indexSize::Float, indexIds::[Int]}
| IndexEmpty {indexSize::Float}
deriving ( Show , Eq )
I derived some thing like this for QuickCheck testing
instance Arbitrary a => Arbitrary ( IntMap a ) where
    arbitrary = liftM IntMap.fromList arbitrary

instance Arbitrary Index where
    arbitrary =
    oneof [ liftM3 Index arbitrary arbitrary arbitrary , liftM2 IndexLeaf arbitrary arbitrary , liftM IndexEmpty arbitrary ]
but its generating infinite list of data. After reading the paper QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs
i tried to write above one using sized but i am not sure how to write this .

instance Arbitrary a => Arbitrary ( IntMap a ) where
    arbitrary = liftM IntMap.fromList arbitrary

instance Arbitrary Index where
    arbitrary = sized arbIndex

arbIndex 0 = liftM IndexEmpty arbitrary
arbIndex 1 = liftM2 IndexLeaf arbitrary arbitrary
arbIndex n = frequency [ ( 1 , liftM IndexEmpty arbitrary ) , ( 1 , liftM2 IndexLeaf arbitrary arbitrary ) , ( 2 , liftM2 Index arbitrary arbitrary ( arbIndex $ div n 2 ) ) ]

but from this type i can see arbIndex $ div n 2 will return Gen Index not Gen ( IntMap Index ) and i am getting compiler error . Could some one please tell me , how to write arbIndex n in terms of smaller n like in the paper
arbTree 0 = liftM Leaf arbitrary
arbTree n = frequency[ ( 1 , liftM Leaf arbitrary ) , ( 4 , liftM2 Branch ( arbTree $ div n 2 ) ( arbTree $ div n 2 ) ) ]

Thank You
Mukesh Tiwari
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