6.001, Spring 2004—Recitation 26 1MASSACHVSETTS INSTITVTE OF TECHNOLOGYDepartment of Electrical Engineering and Computer Science6.001—Structure and Interpretation of Computer ProgramsSpring 2004Recitation 26Explicit Control Evalread-eval-print-loop(perform (op initialize-stack))(perform(op prompt-for-input) (const ";;; EC-Eval input:"))(assign exp (op read))(assign env (op get-global-environment))(assign continue (label print-result))(goto (label eval-dispatch))print-result(perform (op print-stack-statistics))(perform(op announce-output) (const ";;; EC-Eval value:"))(perform (op user-print) (reg val))(goto (label read-eval-print-loop))unknown-expression-type(assign val (const unknown-expression-type-error))(goto (label signal-error))unknown-procedure-type(restore continue)(assign val (const unknown-procedure-type-error))(goto (label signal-error))signal-error(perform (op user-print) (reg val))(goto (label read-eval-print-loop))eval-dispatch(test (op self-evaluating?) (reg exp))(branch (label ev-self-eval))(test (op variable?) (reg exp))(branch (label ev-variable))(test (op quoted?) (reg exp))(branch (label ev-quoted))(test (op assignment?) (reg exp))(branch (label ev-assignment))(test (op definition?) (reg exp))(branch (label ev-definition))(test (op if?) (reg exp))(branch (label ev-if))(test (op lambda?) (reg exp))(branch (label ev-lambda))(test (op begin?) (reg exp))(branch (label ev-begin))(test (op application?) (reg exp))(branch (label ev-application))(goto (label unknown-expression-type))ev-self-eval(assign val (reg exp))(goto (reg continue))ev-variable(assign val (op lookup-variable-value) (reg exp) (reg env))(goto (reg continue))ev-quoted(assign val (op text-of-quotation) (reg exp))(goto (reg continue))ev-lambda(assign unev (op lambda-parameters) (reg exp))(assign exp (op lambda-body) (reg exp))(assign val (op make-procedure)(reg unev) (reg exp) (reg env))6.001, Spring 2004—Recitation 26 2(goto (reg continue))ev-application(save continue)(save env)(assign unev (op operands) (reg exp))(save unev)(assign exp (op operator) (reg exp))(assign continue (label ev-appl-did-operator))(goto (label eval-dispatch))ev-appl-did-operator(restore unev)(restore env)(assign argl (op empty-arglist))(assign proc (reg val))(test (op no-operands?) (reg unev))(branch (label apply-dispatch))(save proc)ev-appl-operand-loop(save argl)(assign exp (op first-operand) (reg unev))(test (op last-operand?) (reg unev))(branch (label ev-appl-last-arg))(save env)(save unev)(assign continue (label ev-appl-accumulate-arg))(goto (label eval-dispatch))ev-appl-accumulate-arg(restore unev)(restore env)(restore argl)(assign argl (op adjoin-arg) (reg val) (reg argl))(assign unev (op rest-operands) (reg unev))(goto (label ev-appl-operand-loop))ev-appl-last-arg(assign continue (label ev-appl-accum-last-arg))(goto (label eval-dispatch))ev-appl-accum-last-arg(restore argl)(assign argl (op adjoin-arg) (reg val) (reg argl))(restore proc)(goto (label apply-dispatch))apply-dispatch(test (op primitive-procedure?) (reg proc))(branch (label primitive-apply))(test (op compound-procedure?) (reg proc))(branch (label compound-apply))(goto (label unknown-procedure-type))primitive-apply(assign val (op apply-primitive-procedure)(reg proc)(reg argl))(restore continue)(goto (reg continue))compound-apply(assign unev (op procedure-parameters) (reg proc))(assign env (op procedure-environment) (reg proc))(assign env (op extend-environment)(reg unev) (reg argl) (reg env))(assign unev (op procedure-body) (reg proc))(goto (label ev-sequence))ev-begin(assign unev (op begin-actions) (reg exp))(save continue)(goto (label ev-sequence))6.001, Spring 2004—Recitation 26 3ev-sequence(assign exp (op first-exp) (reg unev))(test (op last-exp?) (reg unev))(branch (label ev-sequence-last-exp))(save unev)(save env)(assign continue (label ev-sequence-continue))(goto (label eval-dispatch))ev-sequence-continue(restore env)(restore unev)(assign unev (op rest-exps) (reg unev))(goto (label ev-sequence))ev-sequence-last-exp(restore continue)(goto (label eval-dispatch))ev-if(save exp)(save env)(save continue)(assign continue (label ev-if-decide))(assign exp (op if-predicate) (reg exp))(goto (label eval-dispatch))ev-if-decide(restore continue)(restore env)(restore exp)(test (op true?) (reg val))(branch (label ev-if-consequent))ev-if-alternative(assign exp (op if-alternative) (reg exp))(goto (label eval-dispatch))ev-if-consequent(assign exp (op if-consequent) (reg exp))(goto (label eval-dispatch))ev-assignment(assign unev (op assignment-variable) (reg exp))(save unev)(assign exp (op assignment-value) (reg exp))(save env)(save continue)(assign continue (label ev-assignment-1))(goto (label eval-dispatch))ev-assignment-1(restore continue)(restore env)(restore unev)(perform(op set-variable-value!) (reg unev) (reg val) (reg env))(assign val (const ok))(goto (reg continue))ev-definition(assign unev (op definition-variable) (reg exp))(save unev)(assign exp (op definition-value) (reg exp))(save env)(save continue)(assign continue (label ev-definition-1))(goto (label eval-dispatch))ev-definition-1(restore continue)(restore env)(restore unev)(perform(op define-variable!) (reg unev) (reg val) (reg env))(assign val (const ok))(goto (reg continue))6.001, Spring 2004—Recitation 26 4Adding letev-let(save continue)___________(assign argl (op empty-arglist))(assign proc (op binding-names) (reg exp))__________(assign unev (op binding-values) (reg exp))ev-let-operand-loop(save argl)(assign exp (op first-binding) (reg unev))(test (op last-operand?) (reg unev))(branch (label ev-let-last-binding))(save env)(save unev)(assign continue (label ev-let-accumulate-binding))(goto (label eval-dispatch))ev-let-accumulate-binding(restore unev)(restore env)(restore argl)(assign argl (op adjoin-arg) (reg val) (reg argl))(assign unev (op rest-operands) (reg unev))(goto (label ev-let-operand-loop))ev-let-last-binding(assign continue (label ev-let-accum-last-binding))(goto (label eval-dispatch))ev-let-accum-last-binding(restore argl)(assign argl (op adjoin-arg) (reg val) (reg argl))(restore proc)(goto (label ev-final-let))ev-final-let(restore exp)(assign env (op extend-environment)___________________________(assign unev (op let-body) ___________)(goto (label ev-sequence))1. By reference to the rest of EC-eval, and knowledge of thedesugaring of let, where was most of this code appropriatedfrom? (It was copied with label modification from eceval)2. Fill in the blanks.3. There’s a bug in
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