[Omake] How to pass an empty string to concat()?

[Dmitry Bely]

This just does not work:

osh
% d=''
- : <string ''>
       : String
% println($(concat $(d),1 2 3))
1''2''3
% d=$''
% println($(concat $(d),1 2 3))
%
(even worse - here I cannot leave osh normally and can only kill it)

Why I need it? I am trying to write a function that converts
backslashes in the string to forward slashes, e.g.
"c:\some\path" -> "c:/some/path"

As foreach cannot be directly applied to string characters (right?) I
am going to convert string to the sequence, transform it and then
merge back into the string by concat(). Wrong approach?

- Dmitry Bely