RE: can't export conditional variable set with 'cond'

[M]

>I think this has something to do with compilation indeed. More specifically, 
>it is caused by cross module inlining [1]. You probably need to declare your 
>env module as not declarative by setting #:declarative? to #f inside the 
>define-module form of env. I think the compiler inlines varB somehow. Not 
>super sure, I am no Guile expert but you could inspect the assembly for main 
>to see what the compiler did.

You shouldn’t need to do that – definitions / variables that are set! within 
the same module are (modulo bugs, which apparently exist) are (supposedly) 
recognised as non-declarative:

>To allow Guile to reason about the values of top-levels from a module, a 
>module can be marked as declarative. This flag applies only to the subset of 
>top-level definitions that are themselves declarative: those that are defined 
>within the compilation unit, and not assigned (set!) or redefined within the 
>compilation unit. 
> By default, modules are compied declaratively if […].

(Technically it doesn’t say that the compiler will actually act according to 
this flag, but I think it’s clear what’s meant here.)