Emacs version 24.4.1.
I search a lot material, and find the someone have tried below: http://kitchingroup.cheme.cmu.edu/blog/2015/02/02/helm-actions-when-there-is-no-match/
and wikemacs: http://wikemacs.org/wiki/How_to_write_helm_extensions
but could not work for me.
I want to customize helm interface. use selection candidate where there is one, and use user input when there is none. like helm-find-files.
