[Haskell-cafe] ReadP - take first succesful parser ?
marco-oweber at gmx.de
Wed Apr 4 05:31:08 EDT 2007
I want to make the parser
choice [string "dummy", anystring ]
where anystring = many get
return the first match.
(Thus if "dummy" matches disregarg all following
I want to parse some wmii events.
They all look this way
LeftBarClick 1 web
At this moment I only need two of them (FocusTag and UnfocusTag)
So I've created the data type
type O = String
data WMIIEvent = FocusTag Int
| UnfocusTag Int
| Unkown String -- to be implemented
Now I want to create a simple ReadP parser which looks like this:
============= parser code ============================================
instance Read WmiiEvent where
readsPrec _ = readP_to_S (foldr1 takeFirst
[ rp "FocusTag" FocusTag
, rp "UnfocusTag" UnfocusTag
, rpUnkown ])
where rp str f = fmap f $ string str >> skipSpaces >> liftM read (many get)
rp :: (Read a) => String -> (a -> WmiiEvent) -> ReadP WmiiEvent
rpUnkown = (many get) >>= return . Unkown
rpUnkown :: ReadP WmiiEvent
But I'm getting an ambiguous parse. (because "UnfocusTag 3" makes two
parsers of the choice list succeed.
How is this done?
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