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The Java abstract syntax classes include a separate composite hierarchy (called IfForm) for representing boolean expression as conditionals (the type ifExp in boolsimp.ss). This representation includes only three concrete variant classes, making it much easier to write the visitors that perform normalization, evaluation, and clean-up.
The visitor pattern is a straightforward but notationally involved alternative to the interpreter pattern.. You can mechanically translate interpreter pattern code to visitor pattern code. (Perhaps IDEs like Eclipse should support such transformations.) The interpreter solution to this assignment is easier to write than the visitor solution described in the preceding program description. If you are still learning Java mechanics, you are encouraged to write an interpreter solution first and translate it (if you can) to visitor form. A perfect interpreter solution will only be penalized 15% versus a perfect visitor solution. If you submit an interpreter solution, your program must conform to class signatures given in the interpreter pattern support code below (just as a visitor solution must conform to the class signatures given in the visitor pattern code below).
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