[xsmith-dev] Numeric types not playing nice

[William G Hatch]

Hmm, that sounds like a bug.  Can you share a link to your code?

This may be one of those corners of Xsmith that was built out but
never seriously exercised.

On Mon, Jan 15, 2024 at 12:39:31PM +0000, Vree, E.A. de (Everard, Student B-TCS) wrote:
>Hello everyone,
>
>I am currently working on a Haskell fuzzer  and new to Racket and Xsmith in general, so I apologize in advance if this question is trivial. There is something I don't understand about the types in Xsmith:
>I emulate Haskell's numerical types like this:
>
>(define number-type (base-type 'number #:leaf? #f))
>(define real-type (base-type 'real number-type #:leaf? #f))
>(define integral-type (base-type 'integral real-type #:leaf? #f))
>(define int-type (base-type 'int integral-type))
>(define integer-type (base-type 'integer integral-type))
>(define fractional-type (base-type 'fractional real-type #:leaf? #f))
>(define float-type (base-type 'float fractional-type))
>
>I then define the type info from the Minus Expression like this:
>
>(define numeric-bin-op-subtype (λ (n t) (hash 'l t 'r t)))
>
>[Minus [(fresh-subtype-of number-type) numeric-bin-op-subtype]]
>
>My assumption was that both Minus children nodes would be constrained to all the non-leaf nodes in either integral-type, or fractional-type. However, Xsmith still generates Minus nodes with 'l integral and 'r fractional, causing a type constraint violation in Haskell. I have since switched to using (fresh-type-variable integral-type fractional-type). This works, but I am still puzzled about fresh-subtypes. REPL experiments confirm that even fresh-subtypes of my real-types can be unified with both fractional-type and integral-type. What happens when a fresh-subtype is created?
>
>Regards,
>
>Everard de Vree