Not sure about Haskell (what I know about the compilation model makes it seem more difficult), but in a typical Java environment (including an IDE remote debugg

Not sure about Haskell (what I know about the compilation model makes it seem more difficult), but in a typical Java environment (including an IDE remote debugging tomcat/jetty, for instance), the debugger will hot swap changes that are just to method bodies. The sad part is that this encourages bad development practices because piling on nested loops doesn't require bouncing the server, while properly factored code does. There are tools like JRebel that are supposed to fix this, but I haven't used them.