[Haskell-beginners] Parsing

[mike h]

Hi Francesco,
Yes, I think you are right with "Are you sure you are not wanting [String] instead of String?”

I could use Parsec but I’m building up a parser library from first principles i.e.

newtype Parser a = P (String -> [(a,String)])

parse :: Parser a -> String -> [(a,String)]
parse (P p)  = p

and so on…. 

It’s just an exercise to see how far I can get. And its good fun. So maybe I need add another combinator or to what I already have. 

Thanks

Mike


> On 14 Apr 2017, at 19:35, Francesco Ariis <fa-ml at ariis.it> wrote:
> 
> On Fri, Apr 14, 2017 at 07:02:37PM +0100, mike h wrote:
>> 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
> 
> Hello Mike,
> 
>    I am not really sure what you are doing here? You are parsing a dot
> separated list (like.this.one) but at the end you are concatenating all
> together, why?
> Are you sure you are not wanting [String] instead of String?
> 
> If so, Parsec comes with some handy parser combinators [1], maybe one of
> them could fit your bill:
> 
>    -- should work
>    packageP = literal "package" *> Pkg <$> sepEndBy1 identifier (char '.')
> 
> [1] https://hackage.haskell.org/package/parsec-3.1.11/docs/Text-Parsec-Combinator.html <https://hackage.haskell.org/package/parsec-3.1.11/docs/Text-Parsec-Combinator.html>
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