CODEWITHSUNDEEP
inputschemeracket
rnso
rnso

Reputation: 24535

Why this list has only void items in Racket

I tried to have user input function using code on this page: A simple Racket terminal interaction

(define entry_list (for/list ([line (in-lines)]
           #:break (string=? line "done"))
  (println line)))

(println entry_list)

Output is: 

this 
"this "
is 
"is "
a 
"a "
test
"test"
for testing only
"for testing only"
done
'(#<void> #<void> #<void> #<void> #<void>)

Why is the list consisting of only "void" items?

Upvotes: 2

Views: 93

Answers (1)

hugomg
hugomg

Reputation: 69934

That is because the println function returns #<void>. If instead of println you put something that returned a different value for each line you would end up with a more interesting list.

For example, the following code should return a list with the lines that you typed in:

(define entry_list
  (for/list ([line (in-lines)]
             #:break (string=? line "done"))
    line))

If you just want to print the lines then you could have used for instead of for/list, to avoid creating an useless list of voids at the end:

Upvotes: 5

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