Hi,

I think they are useful as other map break functions.
Now I can define them as follows. They can work in 
`\int_step_inline:nnnn`. Although their definitions are a little weird.

\cs_new_nopar:Npn \int_step_break:
   { \__prg_map_break:Nn \scan_stop: { } }
\cs_new_nopar:Npn \int_step_break:n
   { \__prg_map_break:Nn \scan_stop: }

There are some more work in `\int_step_function:nnnN` case.
Maybe I missed something. Please let me know.

Regards,
-- 
Qing Lee