real-time Haskell expression-internal type inference

.vimrc

let g:airline_section_gutter = "%{MyStatuslineFunction()}%="
function! MyStatuslineFunction()
    if &l:ft != "haskell"
        return "nope"
    else
        let l:file = expand("%")
        if l:file == ''
            return ""
        endif
        if !filereadable(l:file)
            return ""
        endif
        let l:line = line('.')
        let l:col = col('.')
        let l:cmd = hdevtools#build_command('type', shellescape(l:file) . ' ' . l:line . ' ' . l:col)
        let l:output = system(l:cmd)
        let l:types = []
        for l:line in split(l:output, '\n')
            let l:m = matchlist(l:line, '\(\d\+\) \(\d\+\) \(\d\+\) \(\d\+\) "\([^"]\+\)"')
            call add(l:types, [l:m[1 : 4], l:m[5]])
        endfor
        return len(types) > 0 ? types[0][1] : "(no type)"
    endif
endfunction

EnlightenedShimmeringHoiho.mp4