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Held: Wednesday, February 28, 2007
Summary: Today we expand our exploration of input and output to include files, particularly how one recurses over files.
read a value and square itproblem in which you repeatedly prompt when given a non-number.
(letrec ((prompt-and-square (lambda () ... ; if it's not a nubmer, try again (prompt-and-square) ...))) (prompt-and-square))
anythingyou can do on the computer.
(write value port)
(display value port)
readdo when there's nothing left in the file? It returns a special value (which DrScheme displays as
(define recursive-proc (lambda (val) (if (base-case-test) (base-case val) (combine (partof val) (recursive-proc (simplify val))))))
(eof-object? (peek-char input-port))
(define recursive-proc (lambda (input-port other-params) (if (eof-object? (peek-char input-port)) (close-and-return input-port (base-case other-params)) (combine (read input-port) (recursive-proc input-port other-params))))) (define close-and-return (lambda (input-port return-value) (close input-port) return-value))
I usually create these pages
on the fly, which means that I rarely
proofread them and they may contain bad grammar and incorrect details.
It also means that I tend to update them regularly (see the history for
more details). Feel free to contact me with any suggestions for changes.
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