Integer generators wrapping at 99?

[Misophistful]

Disclaimer: I'm brand new to simple-check, so there's a very good chance that I've misunderstood how generators should be used.

I'm trying to write a generator that creates a range of positive integers between 0 and 1000. However, my attempt at doing this (gen/sample gen/nat 1000) doesn't generate any integers larger than 99. In fact, when I evaluate (gen/sample gen/nat 101) I can see the 101st value wrapping back around to 0.

Is this expected behaviour? If so, what is an alternative approach for generating positive integers larger than 99?

[reiddraper]

tl;dr, try (gen/sample (gen/choose 0 1000))

There's a couple of things going on that are causing the confusion. First, generators (which are actually functions), accept two parameters under the covers: a random number generator, and a 'size' parameter. The size parameter is used to determine how 'big' the generated value should be. When you run a test, the size parameter starts at 0, and then goes up to 200 (by default). This is done so that we don't start off testing your code with a large collection/value, when it might fail quickly on a small one. Additionally, the gen/int generator uses this size parameter to determine the max value it will generate, in fact, it's defined like this: def int (sized (fn [size] (choose (- size) size))). So by default, gen/int will only generate numbers in the range -200 - 200. I'm thinking about changing this in the future, but I'm not quite sure what the correct behavior should be. In the meantime, if you'd like to generate numbers in a given range, gen/choose is designed for exactly this.

I'm closing the issue, but feel free to keep asking questions here.

[Misophistful]

gen/choose was exactly what I was looking for, thank you.

Though I feel like I'm still misunderstanding something around gen/int and gen/nat, as I still can't get them to generate a number larger than 99 (or smaller than -99). How do I force them to generate numbers in the -200 - 200 range you mentioned?

Also, could you explain the use-case for gen/sample? Is it just a helper function to see the output of a generator, which you only use while developing a test? Or does it have a use in "live" tests?

[reiddraper]

Though I feel like I'm still misunderstanding something around gen/int and gen/nat, as I still can't get them to generate a number larger than 99 (or smaller than -99). How do I force them to generate numbers in the -200 - 200 range you mentioned?

Both gen/sample and core/quick-check will use a size-sequence (just the range 0 -> max-size). They, however, use different max sizes, as you can see here and here. You can always create your own lazy-sequence of randomly generated values like this:

(take 1000 (gen/sample-seq gen/int 1000))

Also, could you explain the use-case for gen/sample? Is it just a helper function to see the output of a generator, which you only use while developing a test? Or does it have a use in "live" tests?

It's intended for use just for developing your generators. I tend to just play with it from the REPL.

[Misophistful]

Thank you for taking the time to explain it to me. Now I understand when to use gen/sample and why it was wrapping at 99.