MASSACHVSETTS INSTITVTE OF TECHNOLOGY Department of Electrical Engineering and Computer Science 6.001—Structure and Interpretation of Computer Programs

Spring 2004

Recitation 26 Explicit Control Eval

read-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))
(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))
                                                             ev-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-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))
                                                             ev-if