I use company mode, here is my setup (don't forget to install nim-mode):
;; Nim (add-to-list 'company-backends 'company-nim) (custom-set-variables '(nim-nimsuggest-path "~/.nimble/bin/nimsuggest")) Run
;; Nim (add-to-list 'company-backends 'company-nim) (custom-set-variables '(nim-nimsuggest-path "~/.nimble/bin/nimsuggest"))