Effects, capabilities, and boxes: from scope-based reasoning to type-based reasoning and back

Reasoning about the use of external resources is an important aspect many practical applications. Effect systems enable tracking such information in types, but at cost complicating signatures common functions. Capabilities coupled with escape analysis offer safety and natural signatures, are often overly coarse grained restrictive. We present System C, which builds on generalizes ideas from type-based demonstrates that capabilities effects can be reconciled harmoniously. By assuming all functions second class, we admit for programs. introducing a notion boxed values, lift restrictions second-class values needing to track degree-of-impurity types. The system expressive enough support effect handlers full capacity. practically evaluate C implementation prove its soundness.