Module Flambda2_terms.Effects

The primitive does not change the observable state of the world. For example, it must not write to any mutable storage, call arbitrary external functions or change control flow (e.g. by raising an exception). Note that allocation is not "No effects" (see below).

It is assumed in Flambda that applications of primitives with no effects, whose results are not used, may be eliminated. It is further assumed that applications of primitives with no effects may be duplicated (and thus possibly executed more than once).

Exceptions arising from allocation points, for example "out of memory" or exceptions propagated from finalizers or signal handlers, are treated as "effects out of the ether" and thus ignored for our determination here of effectfulness. The same goes for floating point operations that may cause hardware traps on some platforms.

The primitive does not change the observable state of the world save for possibly affecting the state of the garbage collector by performing an allocation. Applications of primitives that only have generative effects and whose results are unused may be eliminated by the compiler. However, unlike "No effects" primitives, such applications will never be eligible for duplication.

The argument to Only_generative_effects states whether the returned value from the primitive is mutable.

The primitive may have effects beyond those described by No_effects and Only_generative_effects.