Try breaking it up into pieces. There a literal "package" which is
dropped. There is a first identifier, then there are the rest of the
identifiers (a list), then those two things are combined somehow (with
:).
literal "package" *> (:) <$> identifier <*> restOfIdentifiers
where
restOfIdentifiers :: Applicative f => f [String]
restOfIdentifiers = many ((:) <$> char '.' <*> identifier
I have not tested this code, but it should be close to what you are looking for.
On Fri, Apr 14, 2017 at 2:02 PM, mike h
I have data PackageDec = Pkg String deriving Show
and a parser for it
packageP :: Parser PackageDec packageP = do literal “package" x <- identifier xs <- many ((:) <$> char '.' <*> identifier) return $ Pkg . concat $ (x:xs)
so I’m parsing for this sort of string “package some.sort.of.name”
and I’m trying to rewrite the packageP parser in applicative style. As a not quite correct start I have
packageP' :: Parser PackageDec packageP' = literal "package" >> Pkg . concat <$> many ((:) <$> char '.' <*> identifier)
but I can’t see how to get the ‘first’ identifier into this sequence - i.e. the bit that corresponds to x <- identifier in the monadic version.
in ghci λ-> :t many ((:) <$> char '.' <*> identifier) many ((:) <$> char '.' <*> identifier) :: Parser [[Char]]
so I think that somehow I need to get the ‘first’ identifier into a list just after Pkg . concat so that the whole list gets flattened and everybody is happy!
Any help appreciated.
Thanks Mike
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