In fact string-join
is the right procedure for using in this case, simply use " "
(a single space) as delimiter:
(string-join '("44" "444") " ")
=> "44 444"
Just to clarify: in a list the spaces between elements are not considered part of the list, they're there to separate the elements. For example, all these lists are equal and evaluate to the same value:
'("44""444")
'("44" "444")
'("44" "444")
If for some reason you want to consider the spaces as part of the list then you have to explicitly add them as elements in the list:
(define lst '("a" " " "b" " " "c" " " "d"))
(string-join lst "")
=> "a b c d"