At 04:50 PM 5/15/2001 +1200, Tom Pledger wrote:
I did something similar recently, but took the approach of adding more parameters to newtype Parser, rather than converting it into a class.
Yes, that's how I started.
You could try something similar for your generalisations:
newtype Parser ct r = P (ct -> [(r, ct)]) -- ct: collection of tokens, r: result
This is EXACTLY how I started :)
instance SuitableCollection ct => Monad (Parser ct) where ...
instance SuitableCollection ct => MonadPlus (Parser ct) where ...
item :: Collects ct t => Parser ct t force :: Parser ct r -> Parser ct r first :: Parser ct r -> Parser ct r papply :: Parser ct r -> ct -> [(r, ct)]
The `SuitableCollection' class is pretty hard to define, though. Either it constrains its members to be list-shaped, or it prevents you from reusing functions like `item'. Hmmm... I think I've just stumbled across your reason for treating Parser as a class.
:) Maybe. Thanx for your help, though.
When the input isn't list-shaped, is the activity still called parsing? Or is it a generalised fold (of the input type) and unfold (of the result type)?
Actually, I guess you can call it destructive pattern-matching. Salutaciones, JCAB --------------------------------------------------------------------- Juan Carlos "JCAB" Arevalo Baeza | http://www.roningames.com Senior Technology programmer | mailto:jcab@roningames.com Ronin Entertainment | ICQ: 10913692 (my opinions are only mine) JCAB's Rumblings: http://www.metro.net/jcab/Rumblings/html/index.html