I set myself the exercise of converting k-SAT CNF-formulas to 3-SAT
formulas, a task that most theoretical computer scientists will be familiar
with. For that purpose I defined the spec
(s/def ::literal (s/or :symbol symbol? :negated-symbol (s/spec (s/cat :not
#{'not}
:symbol symbol?))))
(s/def ::disjunction (s/spec (s/cat :or #{'or} :literals (s/+ ::literal))))
(s/def ::cnf-expression (s/spec (s/cat :and #{'and} :disjunctions (s/+
::disjunction))))
Examples for this would be
'(and (or a b c d) (or e f))
'(and (or a b c) (or d) (or e f g h i j))
So basically an AND of ORs. However after running some generative tests my
computer began getting really hot. The problem here isn't that I am trying
to solve an NP-complete problem. I am only testing the reduction. I don't
care at this point whether any of these formulas are actually satisfiable.
The problem turned out to be that test.check was generating absurdly large
CNF-formulas from this spec. I'm talking symbol names ~1000 characters long
and the overall formula containing ~1000 symbols.
I could probably mend this problem by overwriting the appropriate
generators. But seeing how this is the very first spec I'm using for
generative testing and I'm already running into this after just 3 lines of
specs, I can easily imagine that I'd end up peppering every spec I'll ever
write with custom generators saying "this list should only contain 50
elements", "this string should not contain emoji's" etc... And even that
might not suffice once I begin composing specs into larger hierarchies
since the size of the test cases would grow exponentially in the number of
layers of abstraction.
Is there a more workable solution for this problem?
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