completions for evil ex commands

Frank Fischer frank.fischer at
Wed Feb 8 22:17:14 CET 2012

Hi Antono,

Am Wed, 08 Feb 2012 15:51:45 +0300
schrieb antono <self at>:

> Hello, All.
> I'm trying to implement rails.vim clone for evil.
> I would like to know easiest way to feed some completion to
> evil ex commands.


> I have following command:
> (evil-ex-define-cmd "Rcontroller" 'rinari-find-controller)
> What should i do to provide completion for it?

First of all, the completion code is not stable yet in the sense that
I'm going to change the interface a little bit in the near future. But
the general actions to take will remain the same, so everything that
works now should be easily adaptable to the new interface.

In order to get completion working you need two things: an argument
handler doing the completion and a special interactive code that can be
used in commands to tell ex state that this specific completion should
be used (not completely true, the interactive code is optional, see

The argument handler must be defined using
`evil-ex-define-argument-type'. This is a macro taking at least one
argument, the first being a flag, the others depending on that flag, so
it looks like this:

(evil-define-argument-type my-type (flag &rest args)

FLAG is a symbol, on of 'start, 'stop, 'update or 'complete. For
completion only 'complete is important. In this case ARGS are three
arguments STRING PREDICATE FLAG with exactly the same interpretation as
the COLLECTION function in "Programmed completion" (see Emacs Lisp
Manual). You have to implement exactly the requested behavior of this
COLLECTION function. The easiest example is the definition of a
"buffer" argument in "evil-ex.el".
Once the argument-type is defined an interactive code must be specified
using `evil-define-interactive-code' (see "evil-types.el" for most
evil-specific interactive codes). It looks like this:

(evil-define-interactive-code "<mycode>"
  :ex-arg my-type
  (list (when (evil-ex-p) evil-ex-argument)))

This defines an interactive code "<mycode>" that can be used in the
(interactive ...) statement in commands defined with
`evil-define-command'. The property ":ex-arg" connects that interactive
code with the argument-type "my-type" (if no such property is given
then the argument is plain text and has no completion). The body should
evaluate to a list-expression. This list will be passed to a command
using this interactive code as parameter(s) (as usual Emacs interactive
codes do).

Finally you must define a command using this interactive code like this:

(evil-define-command rinari-find-controller (arg)
  (interactive "<mycode>")

When such a command is bound to some ex string the corresponding
argument-handler is called for completion.

Ah, I forgot, it is not really required to define an interactive code.
You could also specify the argument-type directly in the command like

(evil-define-command rinari-find-controller (arg)
  :ex-arg my-type
  (interactive "<a>")

(here <a> is the interactive code for a general ex-argument). But if
you require the same argument type for several commands, defining an
interactive code is easier. And defining an interactive code allows to
generate more than a single argument passed to the command (see, e.g.,
the <r> code for an example).

I hope that gives you a starting point. If you have any questions,
don't hesitate to ask.


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