In contrast to the view of many, programming language theory is very closely intertwined with programming practice. It both drives practice and reacts to practi

In contrast to the view of many, programming language theory is very closely intertwined with programming practice. It both drives practice and reacts to practice. In this particular case I imagine the issue was uncovered some time in the 1970s, which is when lexical scoping came to the fore in Scheme (in the US) and ML (in Europe). It's a fairly natural problem to run into if you're either thinking deeply about the interaction between closures (which capture environments) and loop constructs, or if you're programming in a language that supports these features.