On Saturday 30 June 2007, Claus Reinke wrote:
The standard, naïve approach to monadic parsing is very nice, but inefficient. So *please read* some material based on Hutton&Meijer approach, but don't stay there, read something more modern,
since we thereby seem to have left the phase of simple answers to simple questions;-) i'd like to raise a pet issue of mine. my own first combinator parsers (inspired by Wadler's "How to replace failure by a list of successes", but adapted to a call-by-value language) were based on continuations.
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ok, now everybody has had time to chime in with "monadic parsers are based on continuations" or "continuations are just one specific monad". so let me return to the particular issue i'm interested in: contrary to monadic parsers, those continuation-based parsers had *two* continuations, one for success, one for failure. and that seemed to be a very natural match for the problem.
<snip> Two-continuations is a monad too, right? newtype ContErrorT m alpha = ContErrorT { runContErrorT :: forall beta. (alpha -> m beta) -> (Exception -> m beta) -> m beta } instance Monad m => ContErrorT m where return x = ContErrorT (\ k h -> k x) a >>= f = ContErrorT (\ k h -> runContErrorT a (\ x -> runContErrorT (f x) k h) h) instance Monad m => MonadError Exception (ContError m) where throwError e = ContErroT ( \ k h -> h e) a `catchError` f = ContErrorT (\ k h -> runContErrorT a k (\ e -> runContErrorT (f e) k h)) Am I missing something really obvious here? Jonathan Cast http://sourceforge.net/projects/fid-core http://sourceforge.net/projects/fid-emacs