Compile ActionScript with mxmlc is very slow, because each time the whole code is recompiled. Flex SDK provide tool fcsh shell which can speed up this process by incremental compilation. Unfortunately usage of that shell is inconvinient. Mainly by need to type each time compile 1 command to recompile changed part of code (arrow up to repeat last command doesn’t work). I wrote a script that helps in usage of that shell.
You can find it on github