Transform an unformatted list of items (e.g. considered as char) into a list of comma-separated and/or quote-enhanced items.

%let clist=%list_quote(list, mark=%str(%"), sep=%quote( ), rep=%quote(,));

list : a list of blank separated items/char;
mark : (option) character/string used to quote the items in the output list; default: mark is the double quote "; any type of character can be used, though the macros %str/%quote should be employed to pass it in practice (see examples and notes below); note also the particular case where it is passed as mark=_EMPTY_ then it is set to mark=%quote();
sep : (option) character/string separator in input list; default: %quote( ), i.e. sep is blank;
rep : (option) character/string used to replace the separator in the output list; default: %quote(,), i.e. the output list is comma separated; note that rep=_BLANK_ can also be passed so as to set rep=%quote( ).

clist : output formatted list of items, e.g., comma-separated items/char in between quotes..

With the default settings mark=%str(%"), sep=%quote( ), rep=%quote(,), the following command:

%let list=DE AT BE NL UK SE;

%let clist=%list_quote(&list);

returns: clist="DE","AT","BE","NL","UK","SE", while:

%let clist=%list_quote(&list, mark=_EMPTY_);

returns: clist=DE,AT,BE,NL,UK,SE, and:

%let clist=%list_quote(&list, mark=%quote(*), rep=%quote( ));

returns: clist=*DE* *AT* *BE* *NL* *UK* *SE*.

Finally, note also the following use:

%let var=AGE RB090 HT1 QITILE;

%let per_var=%list_quote(&var, mark=_EMPTY_, rep=%quote(*));

with returns per_var=AGE*RB090*HT1*QITILE.

Run macro %_example_list_quote for more examples.

Note the different use of %quote or %str when the marks/separators are special characters (since it takes effect during macro compilation/execution).
When considering the above-mentioned default settings for mark, rep and sep, this is roughly equivalent to running:

%let clist="%sysfunc(tranwrd(%sysfunc(compbl(&list)),%quote( ),%quote(", ")))";