[converter]Separate let and define about vim-vimlparser

[haya14busa]

Do you mean you want to add other translater or provide traversing utilities for translaters?

This is not needed for VimL->S-like-expression / Python / JavaScript translators.
I'm not sure this is the problem of this repository.

But this should be ...

I don't think so. Translater should translate the script as same as possible basically. (except it's some optimization purpose or some other useful purpose.

[mattn]

Yes, I didn't consider exists().

function! s:foo()
  if v:true
    let s = 1
  endif
  if exists('s')
    " blah blah
  endif
endfunction

We can't translate this into js since script author might expect this behavior as is. So we can't prepend define variable.