Continuation magic of this kind is interesting and useful but only when you don't want to use anything outside the Smalltalk VM (for example some database), whe

Continuation magic of this kind is interesting and useful but only when you don't want to use anything outside the Smalltalk VM (for example some database), when you start to communicate with something external to VM you have only moved problem to different place and probably made it harder to solve. There is reason why call/cc is sometimes called "functional goto". But apart from continuations seaside also provides system to abstract out HTML generation, that not only changes syntax of HTML but also has support for building page from tree of prepared components (like you would construct desktop application). And this HAML thing only seems to change syntax of HTML and not add any similar capability, so comparing it to Seaside probably is misguided.