zing Mutually Referential Abstract Objects: The Value Recursion Challenge Don Syme 1 Microsoft Research, Cambridge, U.K. Mutual dependencies between objects arise frequently in programs, and programmers must typically solve this value recursion by manually filling "initialization holes" to help construct the corresponding object graphs, i.e. null values and/or explicitly mutable locations. This paper aims to augment ongoing theoretical work on value recursion with a description of a semi-safe mechanism for a generalized form of value recursion in an ML-like language, where initialization corresponds to a graph of lazy computations whose nodes are sequentially forced, requiring runtime checks for soundness during initialization in the style of Russo. Our primary contribution is to use the mechanism to develop compelling examples of how the absence recursion leads to real problems in the presence of abstraction boundaries, and give micro-examples that characterize how initiali...