One tricky part is backtracking: ... semantic actions must be
prepared for the possibility that their results will be
discarded. ... A straightforward [solution] is to limit your
semantic actions to building ...an AST node, and [ensuring] the
nodes get cleaned up if they’re not needed. In many cases, it
would be nicer to be able to, say, emit bytecode into a buffer, but
I’m not sure what the interface to that would look like.
Hmmm. I'd thought you were already in the (abstract) process of
building a quasiquoter with alternative, potentially unused,
expansions: so I think you know what an interface might look like,
you just don't know if it's more trouble than it's worth to bootstrap...
-Dave
(emitting HTML or bytecode into a buffer is the monoidal string case;
building an AST is the monadic (monoidal endofunctor) case)
cf http://okmij.org/ftp/tagless-final/course/index.html
(semantic actions are popular because they're normally an effective
deforestation of the text -unfold-> AST -fold-> effects hylomorphism;
if you hooked up a pattern matcher in front of the semantic actions
it might be possible to come up with a tree-awk to decouple the
actions from the parsing, at the risk of reinventing xslt)
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