Using find-variable from exercise 5.41 , rewrite compile-variable and compile-assignment to output lexical-address instructions. In cases where find-variable returns not-found (that is, where the variable is not in the compile-time environment), you should have the code generators use the evaluator operations, as before, to search for the binding. (The only place a variable that is not found at compile time can be is in the global environment, which is part of the run-time environment but is not part of the compile-time environment. Thus, if you wish, you may have the evaluator operations look directly in the global environment, which can be obtained with the operation (op get-global-environment), instead of having them search the whole run-time environment found in env.) Test the modified compiler on a few simple cases, such as the nested lambda combination at the beginning of this section.
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