Programming Languages Exercise 1 Solution

Free Identifiers



Implement the function freeIds, which takes a WAE and produces a set of strings. The set should contain a string for each free identifier in the given WAE.







def freeIds(expr: WAE): Set[String] = ???




test(freeIds(WAE("{with {x 1} {+ x y}}")), Set("y"))




test(freeIds(WAE("{with {z 2} 1}")), Set())







Binding Identifiers



Implement the function bindingIds, which is like freeIds, but the result set contains a string for each binding identifier in the given WAE (whether or not the binding identifier is ever referenced by a bound identifier).







def bindingIds(expr: WAE): Set[String] = ???




test(bindingIds(WAE("{with {x 1} {+ x y}}")), Set("x"))




test(bindingIds(WAE("{with {z 2} 1}")), Set("z"))







Bound Identifiers



Implement the function boundIds, which is like freeIds, but the result set contains a string for each bound identifier in the given WAE.







def boundIds(expr: WAE): Set[String] = ???




test(boundIds(WAE("{with {x 1} {+ x y}}")), Set("x"))




test(boundIds(WAE("{with {z 2} 1}")), Set())




















































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