This paper gives a formal basis for the closure conversion phase of functional programming languages with imperative features, using a graphical semantics for the language. We present normal forms of graphs, one corresponding to procedural languages, and one corresponding to object-oriented languages. Using closure conversion, we can prove normalization results for both normal forms. Thus, we obtain sound algorithms for compiling the language into either procedural or object-oriented code. We discuss efficiency issues of the translation and suggest some improvements on the algorithm.