how to insert new line in vimscript substitiute function - function

Question

I want this sentence:
My, sentence.
To be like this:
My,
sentence.
My function is:
function! ParseLine()
let line = getline(".")
echom line
let parsedLine = substitute(line, ",", "\v\\v\\0\\r\r\\n\r\\<cr>\<cr><cr>\\^M\r&\^#\\^#", "g")
call setline(".", parsedLine)
endfunction
What I get when running this function:
Myvv,^M^M^#^M<cr>^M<cr>^M^M,^#^# sentence.

Answer 1

The easiest way:
function! ParseLine()
exec 's/,\s*/,\r/g'
endfunction
Or if you want to first call substitute() then "set" that line:
function! ParseLine()
let parsedLine = substitute(getline('.'), ',\s*', ',\n', "g")
let o = #o
let #o = parsedLine
normal! V"op
let #o=o
endfunction

Answer 2

The way you are trying to do it is never going to work because you can't use newlines in the setline function.
If you try to use setline on a string that contains a newline you will get an error. However, you could do this with an execute "normal! ..." command:
function! ParseLine()
execute "normal! 0f,a\n"
endfunction
That should find the , and insert a newline after it, giving you the result you want.
Note that you have to use execute "normal! ..." as opposed to normal! ... because normal won't understand that \n is a special character and you would get:
My,\n Sentence