Actually, in my experience, PEGs make parsing not complicated. What kind of visualization tools have you found helpful in manipulating the AST? So far I've found equational reasoning (in my head or on paper) much more helpful than visualization in writing code to manipulate ASTs. And code generation from ASTs does not require a lot of effort when it is not especially difficult; it's really just a tree traversal or two. (As you point out, with optimization it can become arbitrarily difficult.)