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how to iterate through a list in racket? if the character in the list is alphabetic, I want to add to a new string

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0

Here is my code? Can anyone tell me how to iterate through a list? if the character in the list is alphabetic, I want to add to a new string

#lang racket

(define (conversion input)
 (define s (string))
 (let ((char (string->list input)))
 (cond
 [(char-alphabetic? (first (char)))
 (string-append s first)]
 [(char-alphabetic? (rest (char)))
 (string-append s rest)]))
 (display s))

racket

share|improve this question

edited Mar 24 at 22:16

Sylwester

36.6k23058

asked Mar 24 at 20:42

user11104854

add a comment | 

0

Here is my code? Can anyone tell me how to iterate through a list? if the character in the list is alphabetic, I want to add to a new string

#lang racket

(define (conversion input)
 (define s (string))
 (let ((char (string->list input)))
 (cond
 [(char-alphabetic? (first (char)))
 (string-append s first)]
 [(char-alphabetic? (rest (char)))
 (string-append s rest)]))
 (display s))

racket

share|improve this question

edited Mar 24 at 22:16

Sylwester

36.6k23058

asked Mar 24 at 20:42

user11104854

add a comment | 

Here is my code? Can anyone tell me how to iterate through a list? if the character in the list is alphabetic, I want to add to a new string

#lang racket

(define (conversion input)
 (define s (string))
 (let ((char (string->list input)))
 (cond
 [(char-alphabetic? (first (char)))
 (string-append s first)]
 [(char-alphabetic? (rest (char)))
 (string-append s rest)]))
 (display s))

racket

share|improve this question

edited Mar 24 at 22:16

Sylwester

36.6k23058

asked Mar 24 at 20:42

user11104854

#lang racket

(define (conversion input)
 (define s (string))
 (let ((char (string->list input)))
 (cond
 [(char-alphabetic? (first (char)))
 (string-append s first)]
 [(char-alphabetic? (rest (char)))
 (string-append s rest)]))
 (display s))

share|improve this question

edited Mar 24 at 22:16

Sylwester

36.6k23058

asked Mar 24 at 20:42

user11104854

share|improve this question

edited Mar 24 at 22:16

Sylwester

36.6k23058

asked Mar 24 at 20:42

user11104854

edited Mar 24 at 22:16

Sylwester

36.6k23058

edited Mar 24 at 22:16

Sylwester

36.6k23058

1 Answer
1

active

oldest

votes

1

Basic iteration is:

(define (copy-list lst)
 (if (null? lst)
 '()
 (cons (car lst)
 (copy-list (cdr lst))))

(copy-list '(1 2 3)) ; ==> (1 2 3)

This one actually makes a shallow copy of your list. Sometimes you iterate with keeping some variables to accumulate stuff:

(define (sum-list lst acc)
 (if (null lst)
 acc
 (sum-list (cdr lst) (+ acc (car lst)))))

(sum-list '(1 2 3)) ; ==> 6

Looking at these you'll see a pattern emerges so we have made stuff like map, foldl, and foldr to abstract the iteration:

(define (copy-list-foldr lst)
 (foldr cons '() lst)

(define (copy-list-map lst)
 (map values lst))

(define (sum-list-foldl lst)
 (foldl + 0 lst))

Looking at your challenge I bet you can fix it with a foldr.

share|improve this answer

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

add a comment | 

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1

Basic iteration is:

(define (copy-list lst)
 (if (null? lst)
 '()
 (cons (car lst)
 (copy-list (cdr lst))))

(copy-list '(1 2 3)) ; ==> (1 2 3)

This one actually makes a shallow copy of your list. Sometimes you iterate with keeping some variables to accumulate stuff:

(define (sum-list lst acc)
 (if (null lst)
 acc
 (sum-list (cdr lst) (+ acc (car lst)))))

(sum-list '(1 2 3)) ; ==> 6

Looking at these you'll see a pattern emerges so we have made stuff like map, foldl, and foldr to abstract the iteration:

(define (copy-list-foldr lst)
 (foldr cons '() lst)

(define (copy-list-map lst)
 (map values lst))

(define (sum-list-foldl lst)
 (foldl + 0 lst))

Looking at your challenge I bet you can fix it with a foldr.

share|improve this answer

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

add a comment | 

1

Basic iteration is:

(define (copy-list lst)
 (if (null? lst)
 '()
 (cons (car lst)
 (copy-list (cdr lst))))

(copy-list '(1 2 3)) ; ==> (1 2 3)

This one actually makes a shallow copy of your list. Sometimes you iterate with keeping some variables to accumulate stuff:

(define (sum-list lst acc)
 (if (null lst)
 acc
 (sum-list (cdr lst) (+ acc (car lst)))))

(sum-list '(1 2 3)) ; ==> 6

Looking at these you'll see a pattern emerges so we have made stuff like map, foldl, and foldr to abstract the iteration:

(define (copy-list-foldr lst)
 (foldr cons '() lst)

(define (copy-list-map lst)
 (map values lst))

(define (sum-list-foldl lst)
 (foldl + 0 lst))

Looking at your challenge I bet you can fix it with a foldr.

share|improve this answer

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

add a comment | 

Basic iteration is:

(define (copy-list lst)
 (if (null? lst)
 '()
 (cons (car lst)
 (copy-list (cdr lst))))

(copy-list '(1 2 3)) ; ==> (1 2 3)

This one actually makes a shallow copy of your list. Sometimes you iterate with keeping some variables to accumulate stuff:

(define (sum-list lst acc)
 (if (null lst)
 acc
 (sum-list (cdr lst) (+ acc (car lst)))))

(sum-list '(1 2 3)) ; ==> 6

Looking at these you'll see a pattern emerges so we have made stuff like map, foldl, and foldr to abstract the iteration:

(define (copy-list-foldr lst)
 (foldr cons '() lst)

(define (copy-list-map lst)
 (map values lst))

(define (sum-list-foldl lst)
 (foldl + 0 lst))

Looking at your challenge I bet you can fix it with a foldr.

share|improve this answer

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

(define (copy-list lst)
 (if (null? lst)
 '()
 (cons (car lst)
 (copy-list (cdr lst))))

(copy-list '(1 2 3)) ; ==> (1 2 3)

(define (sum-list lst acc)
 (if (null lst)
 acc
 (sum-list (cdr lst) (+ acc (car lst)))))

(sum-list '(1 2 3)) ; ==> 6

(define (copy-list-foldr lst)
 (foldr cons '() lst)

(define (copy-list-map lst)
 (map values lst))

(define (sum-list-foldl lst)
 (foldl + 0 lst))

share|improve this answer

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058

answered Mar 24 at 22:27

SylwesterSylwester

36.6k23058