The semantics of own-variables vividly shows how an at first sight intuitively clean construct is in fact very messy and fraught with subtle ambiguities. Thus it illustrates one kind of insight one can rapidly gain by attempting a formal description. It is true that the various ambiguities were discovered without using any formal methods, but their uncovering took several years. Had a formal semantics been attempted the ambiguities would immediately have revealed themselves and one would have been forced to face and resolve them. Also semantic concepts enable one to concisely and lucidly articulate all the possible interpretations.
The semantics of own-variables requires the use of ’position dependent denotations’ and the techniques to handle these are of some interest in their own right. Although these techniques are not very often useful for describing the conceptual meaning of languages—which is what this book has concentrated on—they are required in describing operational semantics modelling implementations.
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