> Another thing is difference in handling invalid code. A traditional compiler front-end is usually organized as a progression of phases, where each phase takes an unstructured input, checks the input for validity, and, if it is indeed valid, adds more structure on top.

Is this true? The way the d compiler does it is to make a special ast node type called 'error', which allows it to avoid this problem. I have also gotten error messages from c compilers that indicated they were doing something similar.

Now, in the d compiler, this is not a panacea, because erroneous code can cause erroneous error messages about unreachable code, but it generally works quite well.