The built-in indenting in Vim for OCaml seems not very good. How to set up auto indenting for OCaml code in Vim? ocp-indent works very well for me. This posts introduces how to configure Vim to use ocp-indent to automatically indent/format OCaml code.

First, install ocp-indent after installing opam:

$ opam install ocp-indent

Second, configure vim by adding these lines to your ~/.vimrc :

au BufEnter *.ml setf ocaml au BufEnter *.mli setf ocaml au FileType ocaml call FT_ocaml() function FT_ocaml() set textwidth=80 set colorcolumn=80 set shiftwidth=2 set tabstop=2 " ocp-indent with ocp-indent-vim let opamshare=system("opam config var share | tr -d '

'") execute "autocmd FileType ocaml source".opamshare."/vim/syntax/ocp-indent.vim" filetype indent on filetype plugin indent on endfunction

You can use == to format the code selected or the current line now.

Third, to make ocp-indent be automatically invoked by autoindent , add the ocp-indent-vim script. This ensures that ocp-indent will indent the current line after you input Enter, "if", "else", etc. You can use tools like pathogen to manage the installed plugins in Vim.

Last, configuring the ocp-indent by adding these lines to ~/.ocp/ocp-indent.conf" :

# These are `normal`, `apprentice` and `JaneStreet` and set different defaults. JaneStreet