Soundly handling linearity requires special care in the presence of effect handlers, as the programmer may inadvertently compromise the integrity of a linear resource. For instance, duplicating a continuation that closes over a resource can lead to the internal state of the resource being corrupted or discarding the continuation can lead to resource leakage. Thus a naïve combination of linear resources and effect handlers yields an unsound system.

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In the remainder of this blog post we describe a novel approach to rule out such soundness bugs by tracking control-flow linearity, a means to statically assure how often a continuation may be invoked which mediates between linear resources and effectful operations in order to ensure that effect handlers cannot violate linearity constraints on resources. We focus on our implementation in Links. The full technical details are available in our open access POPL’24 distinguished paper Soundly Handling Linearity.