The Proto spatial programming language abstracts the distributed execution of programs as evaluation of spacetime functions over dynamically defined subspaces on a manifold. Previously, however, function evaluation has always been defined in terms of a complete inlining of expressions during compilation. This simplified the definition of programs, at the cost of limiting expressiveness and duplicating code in compiled binaries. In this paper, we address these shortcomings, producing a model of in-place function evaluation and analysis of its implications for Proto. We have extended the MIT Proto compiler and ProtoKernel virtual machine to implement this model, and empirically verified the reduction of compiled binary size.