Language definition by interpreter, translator, continued So far, two ways of looking at MJ for executing codeMJ interpreterMJ translatorMJ translatorFactorial in MJCompiled FactorialCompiled FactorialLooking up vars at runtimeAdding bindings to an environment.. SchemeAdding bindings to a MJ env We need less info for typecheckingProf. Fateman CS 164 Lecture 15 1Language definition by interpreter, translator, continuedLecture 15Prof. Fateman CS 164 Lecture 15 2So far, two ways of looking at MJ for executing code• MJ interpreter (see simple-interp.lisp)• MJ translator into Common Lisp (see simple-translate.lisp)– Common Lisp can be translated into machine languageProf. Fateman CS 164 Lecture 15 3MJ interpreter• Environment includes all Class data• Method calls require setting up a new stack frame– All formal parameters matched to actual parameters– Stack environment then passed to interpreter recursively– Statements in method body evaluated– Return from method call pops frame from stack– To test --Try running (say) Factorial, tracing mj-call or mj-dispatch or mj-new-frame or insert output statements (format t "~%xxx=~s" xxx)Prof. Fateman CS 164 Lecture 15 4MJ translator• Running AST through the translator produces a new (file) of Lisp code.• Environment still has Class methods.• “New” programs produce instances.• Method calls changed into Lisp function calls. • Lisp takes care of all the rest, in particular– All formal parameters matched to actual parameters– Stack environment then passed to interpreter recursively– Statements in method body executed by Lisp– Return from method returns Lisp stack to state previous to method call– Just trace names, e.g. mjl-ClassName-MethodNameProf. Fateman CS 164 Lecture 15 5MJ translator• Consider Factorial.java.• The translator produces about 24 lines of lisp.Prof. Fateman CS 164 Lecture 15 6Factorial in MJclass Factorial{public static void main(String[] a){System.out.println(new Fac().ComputeFac(10));}}class Fac {public int ComputeFac(int num){int num_aux ;if (num < 1)num_aux = 1 ;else num_aux = num * (this.ComputeFac(num-1)) ;return num_aux ;}}Prof. Fateman CS 164 Lecture 15 7Compiled Factorial;; Fac::ComputeFac(defun mjl-Fac-ComputeFac (this L1) ; L1 is num(let ((L2 0)) ; L2 is num_aux(if (< L1 1)(setf L2 1)(setf L2(* L1(let* ((obj this) (vtable (elt obj 0))) ;recursive call. Explain obj(funcall (gethash 'ComputeFac vtable) obj (- L1 1))))))L2));; Vtable for Fac(setf mjl-Fac (make-hash-table))(setf (gethash 'ComputeFac mjl-Fac) #'mjl-Fac-ComputeFac);; Constructor for Fac(defun mjl-Fac+ ()(let ((obj (make-array '(1)))) (setf (elt obj 0) mjl-Fac) obj))Prof. Fateman CS 164 Lecture 15 8Compiled Factorial;; Main routine(format *mj-stdout* "~A~%" ;print the result(let* ((obj (mjl-Fac+)) (vtable (elt obj 0))) ;create a Fac object(funcall (gethash 'ComputeFac vtable) obj 10)))Prof. Fateman CS 164 Lecture 15 9Looking up vars at runtime• Lisp translation makes the separation clear. There are local variables handled by Lisp, and other variables or methods are looked up in the object.• If we are doing our own interpreting, we have two places to look– Local parameters to a method– Vars relative to this. (the object whose method is being called)• Variables in this class• Variables in the parent class(es)Prof. Fateman CS 164 Lecture 15 10Adding bindings to an environment.. Scheme(defun extend-env1 (p1 a1 e);; add one binding to the environment(cons (cons p1 a1) e))(defun extend-env (p a e);; add a list of bindings to the environment. We have two;; variable/value lists. (extend-env '(a b c) '(1 2 3) '((d . 4)));; -> ((a . 1) (b . 2) (c . 3) (d . 4))(if (null p) e(extend-env1 (car p)(car a)(extend-env (cdr p)(cdr a) e))))Prof. Fateman CS 164 Lecture 15 11Adding bindings to a MJ env(defun mj-new-frame(method this actuals e);; pick out the formal args from method.;; we will map them to the actuals.;; make a new env, same as the old layout but with a new frame.;; the frame is an array, and will contain formal <-> actual mapping.;; Make a new environment.. Copy all the old bindings into it and put in;; a few more. It looks like…(cons (layout method) new-frame))Prof. Fateman CS 164 Lecture 15 12We need less info for typechecking• The layout (classes, methods)• The variables: we do not really need space for values (though it won’t hurt much); we need the types and the line/column locations of declarations for error messages.• We don’t need to actually locate (with array offsets etc) the location of values, but if we compute them, we can use this for compiling,
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