VIM: why do these bindings work only sometimes? - vim

Question

I've got these bindings in my .vimrc. They work most of the time, but sometimes they don't: they will just save the file but not run it.
Then I go into insert mode and exit it back to normal mode, and they work again. What could be the problem?
Thanks!
autocmd FileType python map <C-k> :write <CR> :! python % <CR>
autocmd FileType lisp map <C-k> :write <CR> :! clisp % <CR>
autocmd FileType scala map <C-k> :write <CR> :! scala % <CR>

Answer 1

There are many topics to discuss here so with out further ado:
Mappings
Your current mappings map <c-k> ... will only work in normal, visual, and operator-pending modes. However executing your mappings in visual mode or operator-pending modes would save the buffer with only a range of lines (read not good). I suggest you make your mappings for normal mode only.
Two general rules of thumb:
Always supply a mode like n for normal.
Always use noremp instead of map unless you are mapping to a <Plug> mapping.
So one of your mappings might look something similar to this:
nnoremap <c-k> :w<cr>:!python %<cr>
For more information:
:h :map-modes
:h map-overview
:h :nore
:h map-listing
:h map-verbose
Filetype based mappings
You need to do 2 things:
Create a mapping local to a specific buffer by using the <buffer> option for noremap.
Load the mappings for just a specific filetype.
This can be done via an autocmd and FileType event in your .vimrc like so:
autocmd FileType python nnoremap <buffer> <c-k> :w<cr>:!python %:p<cr>
The other way option is by creating a filetype plugin. (see :h ftplugin for more details)
A simple example is do create a file named, ~/.vim/ftplugin/python.vim and place your mappings inside like so:
nnoremap <buffer> <c-k> :w<cr>:!python %:p<cr>
I personally lean more towards the ftplugin approach but having a everything in your .vimrc file can be nice.
For more help see:
:h :au
:h FileType
:h map-local
:h ftplugin
:make
A more vim like way of doing this would be to use :make. (Assuming you want to lint vs execute your current buffer)
:make will execute the 'makeprg'. It defaults to make which is great of C projects
After running :make the quickfix list will be contain any errors.
Set your compiler via the :compiler command.
Extra parameter can be passed like so :make foo-command
Current filename can be represented by %. e.g. :make %
Often people set do :complier/'makeprg' in side of ftplugins e.g. ~/.vim/ftplugin/perl.vim or autocmd's e.g. autocmd FileType perl compiler perl.
Fop more help see:
:h :make
:h 'makeprg'
:h :compiler
:h c_%
quickfix list
Use :cnext and :cprev to move between your errors.
:copen to open up the quickfix list in a window (:cclose to close)
:cwindow to open quickfix list window only if there are errors
May want to use better mappings for :cnext and friends. I suggest Tim Pope's unimpaired plugin
For more help see the following:
:h quickfix
:h :cnext
:h :cope
Alternatives to using :make
Just use <c-z> to suspend vim and run your build system. (Cons: loose out on the quickfix list)
Use :! to compile. (Same cons as suspending) e.g. :!make
Syntastic is a syntax checking system that checks files on save
Ale (Asynchronous Lint Engine) is a plugin for providing linting in NeoVim and Vim 8 while you edit your text files
Dispatch can be used to run things in the background. Great for test suites
May want to consider terminal multiplexers like tmux or screen.
SingleComplile tries and takes some of the work out of using :make
Conclusion
Personally I would install ALE as this removes the need for your mappings. It is also a great idea to learn how to use the location (or quickfix) list. When you are ready to get your hands dirty then you can learn and use :make.
tl;dr
Install ALE.

Answer 2

The space inserted between <CR> and : could lead to errors, because this space is really entered during the execution of the mapping.
With :noremap or :nnoremap (which should be used most of the times, as Peter Rincker wrote in his answer), it wouldn't be a big problem, since it only would move the cursor one char to the right (see :h <space>).
But with :map, it could trigger a custom mapping (or a partial one).
Then, instead of:
autocmd FileType python map <C-k> :write <CR> :! python % <CR>
the following would be better:
autocmd FileType python map <C-k> :write <CR>:! python % <CR>
and this one, really better:
autocmd FileType python nnoremap <C-k> :write <CR>:! python % <CR>