Dr. Philip Cannata 1 Programming Languages Chapter 19 - Continuations.
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Dr. Philip Cannata Programming Languages Chapter 19 - Continuations
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Dr. Philip Cannata 3 (define (f n) (let/cc esc (/ 1 (if (zero? n) (esc 1) n)))) When you invoke the continuation, it’s as if the entire let/cc expression that binds esc should be cut out of the program and replaced with the value passed to esc, i.e., its as if the actual code for f is really this: (define (f n) 1) Exceptions
Transcript of Dr. Philip Cannata 1 Programming Languages Chapter 19 - Continuations.
Dr. Philip Cannata 1
Programming Languages
Chapter 19 - Continuations
Dr. Philip Cannata 2
(define (f n) (let/cc esc (/ 1 (if (zero? n) (esc 1) n))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (f 0)1> (f 2)1/2> (f 1)1>
Exceptions
Dr. Philip Cannata 3
(define (f n) (let/cc esc (/ 1 (if (zero? n) (esc 1) n))))
When you invoke the continuation, it’s as if the entire let/ccexpression that binds esc should be cut out of the program and replaced with the value passed to esc, i.e., itsas if the actual code for f is really this:(define (f n) 1)
Exceptions
Dr. Philip Cannata 4
(define (f n) (+ n (let/cc k (- 5 (k 5)))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (f 6)11>
Escaping Procedures
Dr. Philip Cannata 5
(define route-producer (local ([define resume (box false)]) (lambda (real-send) (local ([define send (lambda (value-to-send) (let/cc k (begin (set-box! resume k) (real-send value-to-send))))]) (if (unbox resume) ((unbox resume) 'dummy) (begin (send 'providence) (send 'houston) (send 'bangalore)))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes. > (let/cc k (route-producer k))'providence> (let/cc k (route-producer k))'houston> (let/cc k (route-producer k))'bangalore> (let/cc k (route-producer k))'dummy
Producers and Consumers
We’ll see thesedetails in a few slides
Dr. Philip Cannata 6
CREATE TABLE EMP (EMPNO NUMBER(7) NOT NULL, CONSTRAINT emp_pkey PRIMARY KEY (empno), ENAME VARCHAR2(10), JOB VARCHAR2(9), MGR NUMBER(4), HIREDATE DATE, SAL NUMBER(7, 2), COMM NUMBER(7, 2), DEPTNO NUMBER(2));
INSERT INTO EMP VALUES (7369, 'SMITH', 'CLERK', 7902, TO_DATE('17-DEC-1980', 'DD-MON-YYYY'), 800, NULL, 20);INSERT INTO EMP VALUES (7499, 'ALLEN', 'SALESMAN', 7698, TO_DATE('20-FEB-1981', 'DD-MON-YYYY'), 1600, 300, 30);INSERT INTO EMP VALUES (7521, 'WARD', 'SALESMAN', 7698, TO_DATE('22-FEB-1981', 'DD-MON-YYYY'), 1250, 500, 30);INSERT INTO EMP VALUES (7566, 'JONES', 'MANAGER', 7839, TO_DATE('2-APR-1981', 'DD-MON-YYYY'), 2975, NULL, 20);INSERT INTO EMP VALUES (7654, 'MARTIN', 'SALESMAN', 7698, TO_DATE('28-SEP-1981', 'DD-MON-YYYY'), 1250, 1400, 30);INSERT INTO EMP VALUES (7698, 'BLAKE', 'MANAGER', 7839, TO_DATE('1-MAY-1981', 'DD-MON-YYYY'), 2850, NULL, 30);INSERT INTO EMP VALUES (7782, 'CLARK', 'MANAGER', 7839, TO_DATE('9-JUN-1981', 'DD-MON-YYYY'), 2450, NULL, 10);INSERT INTO EMP VALUES (7788, 'SCOTT', 'ANALYST', 7566, TO_DATE('09-DEC-1982', 'DD-MON-YYYY'), 3000, NULL, 20);INSERT INTO EMP VALUES (7839, 'KING', 'PRESIDENT', NULL, TO_DATE('17-NOV-1981', 'DD-MON-YYYY'), 5000, NULL, 10);INSERT INTO EMP VALUES (7844, 'TURNER', 'SALESMAN', 7698, TO_DATE('8-SEP-1981', 'DD-MON-YYYY'), 1500, NULL, 30);INSERT INTO EMP VALUES (7876, 'ADAMS', 'CLERK', 7788, TO_DATE('12-JAN-1983', 'DD-MON-YYYY'), 1100, NULL, 20);INSERT INTO EMP VALUES (7900, 'JAMES', 'CLERK', 7698, TO_DATE('3-DEC-1981', 'DD-MON-YYYY'), 950, NULL, 30);INSERT INTO EMP VALUES (7902, 'FORD', 'ANALYST', 7566, TO_DATE('3-DEC-1981', 'DD-MON-YYYY'), 3000, NULL, 20);INSERT INTO EMP VALUES (7934, 'MILLER', 'CLERK', 7782, TO_DATE('23-JAN-1982', 'DD-MON-YYYY'), 1300, NULL, 10);
Producers and Consumers – Oracle sequence exampledrop sequence emp_empno;create sequence emp_empnostart with 1 increment by 1 nomaxvalue;
create or replace trigger emp_empno_triggerbefore insert on empfor each rowbeginselect emp_empno.nextval into :new.empno from dual;end;
Dr. Philip Cannata 7
Producers and Consumers – Oracle sequence example
Dr. Philip Cannata 8
(define (f n) (let/cc esc (/ 1 (if (zero? n) (esc 1) n))))1. When you invoke the continuation, it’s as if the entire let/ccexpression that binds esc should be cut out of the program and replaced with the value passed to esc, i.e., itsas if the actual code for f is really this:(define (f n) 1)2. let/cc binds its variable to the next sexp when it is invoked.3. let/cc causes the interpreter to revert to the state that it was in when the let/cc was defined when the let/cc variable is invoked.
Continuations
Dr. Philip Cannata 9
(define (route-producer send) (begin (send 'providence) (send 'houston) (send 'bangalore)))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (route-producer display)providencehoustonbangalore> (let/cc k (route-producer k))'providence> (let/cc k (route-producer k))'providence
Producers and Consumers
Dr. Philip Cannata 10
(define route-producer (local ([define resume (box false)]) (lambda (send) (if (unbox resume) ((unbox resume) 'dummy) (begin (send 'providence) (send 'houston) (send 'bangalore))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (let/cc k (route-producer k))'providence> (let/cc k (route-producer k))'providence
Producers and Consumers
Dr. Philip Cannata 11
(define route-producer (local ([define resume (box false)]) (lambda (send) (if (unbox resume) ((unbox resume) 'dummy) (begin (send (unbox resume)) (send 'houston) (send 'bangalore))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (let/cc k (route-producer k))false>
Producers and Consumers
Dr. Philip Cannata 12
(define route-producer (local ([define resume (box false)]) (lambda (real-send) (local ([define send (lambda (value-to-send) (let/cc k (begin (set-box! resume k) (real-send value-to-send))))]) (if (unbox resume) ((unbox resume) 'dummy) (begin (send 'providence) (send 'houston) (send 'bangalore)))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes. > (let/cc q (route-producer q))'providence> (let/cc q (route-producer q))'houston> (let/cc q (route-producer q))'bangalore> (let/cc q (route-producer q))'dummy
Producers and Consumers
Dr. Philip Cannata 13
(define route-producer (local ([define resume (box false)]) (lambda (real-send) (local ([define send (lambda (value-to-send) (let/cc k (begin (set-box! resume k) (real-send value-to-send))))]) (if (unbox resume) ((unbox resume) 'dummy) (begin (send 'providence) (send 'houston) (send 'bangalore)))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes.> (route-producer display)providencehoustonbangalore> (route-producer display)'dummy> (route-producer display)'dummy
Producers and Consumers
Dr. Philip Cannata 14
(define route-producer (local ([define resume (box false)]) (lambda (real-send) (local ([define send (lambda (value-to-send) (let/cc k (begin (set-box! resume k) (real-send value-to-send))))]) (if (unbox resume) ((unbox resume) 'dummy) (begin (send 'providence) (send 'houston) (send 'bangalore)))))))
Welcome to DrScheme, version 4.2.1 [3m].Language: PLAI Scheme; memory limit: 256 megabytes. > (let/cc q (route-producer q))'providence> (let/cc q (route-producer q))'houston> (let/cc q (route-producer q))'bangalore> (let/cc q (route-producer q))'dummy
Producers and Consumers
1. What will this do? (let ((a 1)) (display (let/cc q (route-producer q))) (display a) (display " ") (let ((a 2)) (display a)))2. What will this do?(let ((a 1)) (display (let/cc q (route-producer q))) (display a) (display " ") (let ((a 2)) (route-producer display) (display a)))
Run 1. and then run 2.
Then restart and just run 2.
Dr. Philip Cannata 15
(define (make-producer body) (define resume (box false)) (lambda (real-send) (define send-to (box real-send)) (define (send value-to-send) (set-box! send-to (let/cc k (begin (set-box! resume k) ((unbox send-to) value-to-send))))) (if (unbox resume) ((unbox resume) real-send) (body send))))(define number-producer (make-producer (lambda (send) (begin (send 1) (send 2) (send 3)))))
(define get call/cc)
(get number-producer)
Producers and Consumers
press “Run”> (+ (get number-producer) (get number-producer) (get number-producer) )6>press “Run”> (+ (get number-producer) (get number-producer) (get number-producer) (get number-producer)). . user break>
Dr. Philip Cannata 16
(define (make-producer body) (define resume (box false)) (lambda (real-send) (define send-to (box real-send)) (define (send value-to-send) (set-box! send-to (let/cc k (begin (set-box! resume k) ((unbox send-to) value-to-send))))) (if (unbox resume) ((unbox resume) real-send) (body send))))
(define (odds-producer-body send) (local ([define (loop n) (begin (send n) (loop (+ n 2)))]) (loop 1)))
(define odds-producer (make-producer odds-producer-body))
(define (get producer) (let/cc k (producer k)))
Producers and Consumers
press “Run”
> (+ (get odds-producer) (get odds-producer) (get odds-producer) (get odds-producer) (get odds-producer))25>
Dr. Philip Cannata 17
(define (make-producer body) (define resume (box false)) (lambda (real-send) (define send-to (box real-send)) (define (send value-to-send) (set-box! send-to (let/cc k (begin (set-box! resume k) ((unbox send-to) value-to-send))))) (if (unbox resume) ((unbox resume) real-send) (body send))))
(define (integer-producer-body send) (local ([define (loop n) (begin (send n) (loop (+ n 1)))]) (loop 1)))
(define integer-producer (make-producer integer-producer-body))
(define (get producer) (let/cc k (producer k)))
(define (Loop n) (define integer-producer (make-producer integer-producer-body)) (define List (box (list))) (let y ((x n)) (set-box! List (cons (get integer-producer) (unbox List ))) (if (> x 1) (y (- x 1) ) (begin (display (unbox List)) (newline) (eval (cons '* (unbox List)))))))
Producers and Consumers
