In CLIM 2.0, the following should work:
(defun edit-text (stream text)
(accepting-values (stream :own-window t)
(setq text (accept 'string
:stream stream
:view '(text-editor-view
:nlines 20 :ncolumns 40)
:default text)))
text)
Just call edit-text with a CLIM stream and the initial text