Automatically capitalize the first letter of sentence in Vim

Question

When writing in MS Word, or in Open Office, the first letter of each sentence is capitalized automatically by the editor, without needing to press the Shift key. This makes typing much easier.

Is there a script, mode or something that will cause Vim to likewise capitalize the first letter of all sentences automatically, as you type?

Answer 1

This can be done with :help :map-expr mappings for all lowercase characters that check for a preceding end of a sentence. If there's a sentence-ending character before the cursor, it returns the uppercase character, else the typed lowercase character.

You can force a lowercase character after a sentence-ending character by pressing Shift while typing the character. I.e., in effect case is "toggled" for the first letter.

I use a loop to build the individual mappings:

for char in split('abcdefghijklmnopqrstuvwxyz', '\zs')
    exe printf("inoremap <expr> %s search('[.!?]\\_s\\+\\%%#', 'bcnw') ? '%s' : '%s'", char, toupper(char), char)
endfor

for char in split('ABCDEFGHIJKLMNOPQRSTUVWXYZ', '\zs')
    exe printf("inoremap <expr> %s search('[.!?]\\_s\\+\\%%#', 'bcnW') ? '%s' : '%s'", char, tolower(char), char)
endfor

Answer 2

I think for this I would use an InsertCharPre autocmd to check for the beginning of a sentence, and convert v:char to uppercase if found.

I stole the regex for finding a end of sentence from Ingo's answer, and tweaked it to also work on the very first line of the file. This is what I came up with:

augroup SENTENCES
  au!
  autocmd InsertCharPre * if search('\v(%^|[.!?]\_s)\_s*%#', 'bcnw') != 0 | let v:char = toupper(v:char) | endif
augroup END

Note, you can manually bypass the autocmd (or a mapping) to insert a lowercase character, if you type CTRL+V before entering the character to insert it literally. Unless of course you've remapped CTRL+V to something else, like paste. Then you should be able to use CTRL+Q instead.