Vim script: How to easily pipe data into the cwindow - error-handling

Question

I use a custom function (currently residing in .vimrc) and not :make or another direct command line tool to compile/check my currently edited file for errors. Like this:
function! CompileMyCode(...)
set errorformat=Error:\ %m\\,\ in\ line\ %l
let l:output = "Error: bad code!, in line 9"
return l:output
endfunction
command! -nargs=* CompileMyCode :call CompileMyCode(<f-args>)
when using the new command in command mode, no error window shows up.
:CompileMyCode | cwindow
What am I doing wrong?
Edit:
I now tried the following which also does not open any cwindow.
function! CompileMyCode(...)
set errorformat=Error:\ %m\\,\ in\ line\ %l
let l:output = "Error: bad code!, in line 9"
" I tried both of the following lines separately
cexpr l:output
call setqflist([l:output])
endfunction
The proposed commands cexpr and setqflist() do not open the cwindow correctly in my example. Maybe somebody can propose a complete solution?
Edit 2:
The main problem is solved. Here is my current code:
let l:result = expand("%").'|8| errortext'
cexpr [ l:result, l:result ]
caddexpr ''
cwindow
This example respects a default error format that vim seems to support. When cexpring the actual error output and using an errorformat the cwindow seems to ignore that.
Nevertheless, I wanted stick to a default error format anyway in the output, not having to rely on a custom errorformat
Thx for your answers!

Answer 1

I did something similar using cexpr l:output instead of returning the string and that placed the output of the compile in the quickfix window. You can see my vim function here: http://www.zenskg.net/wordpress/?p=199
Update
Adding a blank line to the quickfix list seems to allow the cwindow to appear. For example:
function! MyCompile()
let l:output = "Error: line 1"
cexpr l:output
caddexpr ""
cwindow
endfunction

Answer 2

If you already have access to the error information as structured data in Vim (or can easily obtain it), you can use setqflist().