[ESS] Why is C-c C-l so fast?

[Richard M. Heiberger]

It uses a different technology.

On Windows, and I think on Unix, ESS C-c C-n and C-c C-r sends over one line,
waits for an acknowledgement, then sends the next.

C-c C-l sends over a single line, an instruction to the S language source()
command.  All the work is now done within S-Plus or R directly from the
source file.  There is no interprocess I/O.

Rich