148 lines
4.8 KiB
Scheme
148 lines
4.8 KiB
Scheme
(load "misc/evaluator.scm")
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(display "\nex-4.22 - let\n")
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(display "[answered]\n")
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; Since we have implemented let as a transformation we can simply analyze the
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; transformed expression: ((let? exp) (analyze (let->combination exp)))
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(display "\nex-4.23\n")
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(display "[answered]\n")
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; Implementation from book
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(define (analyze-sequence exps)
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(define (sequentially proc1 proc2)
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(lambda (env) (proc1 env) (proc2 env)))
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(define (loop first-proc rest-procs)
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(if (null? rest-procs)
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first-proc
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(loop (sequentially first-proc (car rest-procs))
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(cdr rest-procs))))
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(let ((procs (map analyze exps)))
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(if (null? procs)
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(error "Empty sequence -- ANALYZE"))
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(loop (car procs) (cdr procs))))
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; Alyssa's implementation
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(define (analyze-sequence exps)
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(define (execute-sequence procs env)
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(cond ((null? (cdr procs)) ((car procs) env))
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(else ((car procs) env)
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(execute-sequence (cdr procs) env))))
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(let ((procs (map analyze exps)))
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(if (null? procs)
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(error "Empty sequence -- ANALYZE"))
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(lambda (env) (execute-sequence procs env))))
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; Alyssa's implementation iterates over the sequence at runtime, while the
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; implementation from the book returns a fully unrolled procedure. Hence,
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; Alyssa's implementation is more expensive because it traverses the list at
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; runtime and needs to do the condition checking.
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(display "\nex-4.24\n")
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(let ((start-time (runtime)))
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(eval '(define (fib n) (if (< n 2) 1 (+ (fib (- n 1)) (fib (- n 2))))) the-global-environment)
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(eval '(fib 20) the-global-environment)
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(display "[eval only] (fib 20) ")
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(display (- (runtime) start-time))
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(display "s\n"))
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(define (analyze-sequence exps)
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(define (sequentially proc1 proc2)
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(lambda (env) (proc1 env) (proc2 env)))
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(define (loop first-proc rest-procs)
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(if (null? rest-procs)
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first-proc
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(loop (sequentially first-proc (car rest-procs))
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(cdr rest-procs))))
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(let ((procs (map analyze exps)))
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(if (null? procs)
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(error "Empty sequence -- ANALYZE"))
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(loop (car procs) (cdr procs))))
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(define (eval exp env)
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((analyze exp) env))
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(define (analyze exp)
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(cond ((self-evaluating? exp)
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(analyze-self-evaluating exp))
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((quoted? exp) (analyze-quoted exp))
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((variable? exp) (analyze-variable exp))
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((assignment? exp) (analyze-assignment exp))
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((definition? exp) (analyze-definition exp))
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((if? exp) (analyze-if exp))
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((lambda? exp) (analyze-lambda exp))
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((begin? exp) (analyze-sequence (begin-actions exp)))
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((cond? exp) (analyze (cond->if exp)))
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((application? exp) (analyze-application exp))
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(else
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(error "Unknown expression type -- ANALYZE" exp))))
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(define (analyze-self-evaluating exp)
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(lambda (env) exp))
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(define (analyze-quoted exp)
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(let ((qval (text-of-quotation exp)))
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(lambda (env) qval)))
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(define (analyze-variable exp)
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(lambda (env) (lookup-variable-value exp env)))
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(define (analyze-assignment exp)
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(let ((var (assignment-variable exp))
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(vproc (analyze (assignment-value exp))))
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(lambda (env)
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(set-variable-value! var (vproc env) env)
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'ok)))
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(define (analyze-definition exp)
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(let ((var (definition-variable exp))
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(vproc (analyze (definition-value exp))))
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(lambda (env)
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(define-variable! var (vproc env) env)
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'ok)))
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(define (analyze-if exp)
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(let ((pproc (analyze (if-predicate exp)))
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(cproc (analyze (if-consequent exp)))
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(aproc (analyze (if-alternative exp))))
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(lambda (env)
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(if (true? (pproc env))
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(cproc env)
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(aproc env)))))
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(define (analyze-lambda exp)
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(let ((vars (lambda-parameters exp))
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(bproc (analyze-sequence (lambda-body exp))))
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(lambda (env) (make-procedure vars bproc env))))
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(define (analyze-application exp)
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(let ((fproc (analyze (operator exp)))
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(aprocs (map analyze (operands exp))))
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(lambda (env)
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(execute-application (fproc env)
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(map (lambda (aproc) (aproc env))
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aprocs)))))
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(define (execute-application proc args)
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(cond ((primitive-procedure? proc)
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(apply-primitive-procedure proc args))
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((compound-procedure? proc)
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((procedure-body proc)
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(extend-environment (procedure-parameters proc)
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args
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(procedure-environment proc))))
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(else
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(error
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"Unknown procedure type -- EXECUTE-APPLICATION"
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proc))))
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(let ((start-time (runtime)))
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(eval '(define (fib n) (if (< n 2) 1 (+ (fib (- n 1)) (fib (- n 2))))) the-global-environment)
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(eval '(fib 20) the-global-environment)
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(display "[eval and analyze] (fib 20) ")
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(display (- (runtime) start-time))
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(display "s\n"))
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