Options.hs

module GLL.Combinators.Options where

-- | Options datatype
--      * left_biased_choice: see function leftBiased
--      * pivot_select: provide a filtering function on `pivots'
data PCOptions = PCOptions  { left_biased_choice    :: Bool
                            , pivot_select          :: Maybe ([Int] -> [Int])
                            }

-- | The default options: no disambiguation
defaultOptions :: PCOptions
defaultOptions = PCOptions False Nothing

-- | Perform a disambiguation similar to 'longest-match'
maximumPivot :: PCOptions -> PCOptions
maximumPivot opts = opts {pivot_select = Just op}
 where  op [] = []
        op xs = (:[]) $ maximum xs

-- | Make the <|> combinator left-biased such that it
--  only returns results of the right child if the left
--  child does not has any results.
leftBiased :: PCOptions
leftBiased = defaultOptions { left_biased_choice = True }