On Sat, Mar 8, 2008 at 9:56 AM, Johan Tibell <[EMAIL PROTECTED]> wrote:
> My current implementation of the parser type is
>
> newtype Parser r a = Parser
> { unParser :: S -> (a -> S -> Result r) -> (S -> Result r) -> Result r }
>
> where the first parameter is the parse state, the second a success
> continuation, and the third a failure continuation. The only tricky
> part (except for the above mentioned problem) is to implement the
> choice operator. I implement mine as
>
> instance Applicative (Parser r) where
> pure a = ...
> p <*> p' = Parser $ \s succ fail ->
> flip (unParser p s) fail $ \f s' ->
> unParser p' s' (succ . f) fail
Copied the wrong code, here's the implementation of <|>
instance Alternative (Parser r) where
empty = ...
p <|> p' = Parser $ \s@(S _ pos) succ fail ->
unParser p s succ $ \s'@(S _ pos') ->
if pos == pos'
then unParser p' s' succ fail
else fail s'
-- Johan
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