Does this look correct for an `Arb frequency` function And w kotlinlang #kotest

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Title

s

simon.vergauwen

06/06/2020, 2:19 PM

Does this look correct for an

Arb.frequency

function? And would there be any interest for this operator? You could easily derive

choice

from this operator. It was inspired by

frequency

from

ScalaTest

, in contrast to

choice

it takes a

weight

per

Arb

.

s

sam

06/06/2020, 5:36 PM

We have Arb.choose, is that sufficient for what you need?

/**
 * Returns a stream of values based on weights:
 *
 * Arb.choose(1 to 'A', 2 to 'B') will generate 'A' 33% of the time
 * and 'B' 66% of the time.
 *
 * @throws IllegalArgumentException If any negative weight is given or only
 * weights of zero are given.
 */
fun <A : Any> Arb.Companion.choose(a: Pair<Int, A>, b: Pair<Int, A>, vararg cs: Pair<Int, A>)

s

simon.vergauwen

06/07/2020, 8:08 AM

No, that isn’t sufficient for me. I’m using this to create an

Arb

from a

sealed class

but I want the create an

Arb

for every case, and I don’t want them to occur in the same frequency. Example:

fun <A> pureIO(arb: Arb<A>): Arb<IO<A>> = arb.map { IO.just(it) }
fun failingIO(): Arb<IO<Nothing>> = Arb.throwable().map { IO.raiseError(it) }

fun <A> <http://Arb.Companion.io|Arb.Companion.io>(arb: Arb<A>): Arb<IO<A>> =
 Arb.frequency(5 to pureIO(arb), 1 to failingIO())

s

sam

06/07/2020, 9:32 AM

Thats what choose does?

s

simon.vergauwen

06/07/2020, 9:33 AM

Yes, but based on

not on

Arb<A>

Pair<Int, A>

vs

Pair<Int, Arb<A>>

s

sam

06/07/2020, 11:22 AM

Oh

I have added to master a version that accepts arbs rather than values. I've also added in aliases to frequency to aid discoverability for those from a haskell quickcheck background. https://github.com/kotest/kotest/issues/1499

s

simon.vergauwen

06/07/2020, 6:27 PM

Awesome 🙌

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