Hi,

> +    (inputs
> +     `(("bison" ,bison)
> +       ("flex" ,flex)

"bison" and "flex" are usually only used at compile time,
so these should probably be native inputs.  As a test,
you can use "guix gc --references" to test if a reference to
"bison" and "flex" is retained (if there's no reference,
then they should probably be native-inputs).

Greetings,
Maxime.