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86 lines
3.4 KiB
Haskell
86 lines
3.4 KiB
Haskell
module Range where
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import qualified Data.Char as Char
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import Data.List (span)
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import Data.List.NonEmpty (nonEmpty)
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import Data.Semigroup
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import Data.String
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import Prologue
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import Test.LeanCheck
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-- | A half-open interval of integers, defined by start & end indices.
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data Range = Range { start :: Int, end :: Int }
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deriving (Eq, Show, Generic)
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-- | Make a range at a given index.
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rangeAt :: Int -> Range
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rangeAt a = Range a a
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-- | Return the length of the range.
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rangeLength :: Range -> Int
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rangeLength range = end range - start range
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-- | Offset a range by a constant delta.
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offsetRange :: Range -> Int -> Range
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offsetRange a b = Range (start a + b) (end a + b)
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-- | Divide a range in two at the given coordinate.
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--
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-- Passing a coordinate that does not lie between start and end will result in one of the ranges being empty.
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divideRange :: Range -> Int -> (Range, Range)
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divideRange Range{..} at = (Range start divider, Range divider end)
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where divider = max (min end at) start
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-- | Break a string down into words and sequences of punctuation. Return a list
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-- | strings with ranges, assuming that the first character in the string is
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-- | at the given index.
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rangesAndWordsFrom :: Int -> String -> [(Range, String)]
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rangesAndWordsFrom _ "" = []
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rangesAndWordsFrom startIndex string = fromMaybe [] $ take isWord <|> take isPunctuation <|> skip Char.isSpace
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where
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save parsed = (Range startIndex $ endFor parsed, parsed)
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take = parse (Just . save)
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skip = parse (const Nothing)
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endFor parsed = startIndex + length parsed
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parse transform predicate = case span predicate string of
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([], _) -> Nothing
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(parsed, rest) -> Just . maybe identity (:) (transform parsed) $ rangesAndWordsFrom (endFor parsed) rest
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-- | Is this a word character?
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-- | Word characters are defined as in [Ruby’s `\p{Word}` syntax](http://ruby-doc.org/core-2.1.1/Regexp.html#class-Regexp-label-Character+Properties), i.e:.
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-- | > A member of one of the following Unicode general category _Letter_, _Mark_, _Number_, _Connector_Punctuation_
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isWord c = Char.isLetter c || Char.isNumber c || Char.isMark c || Char.generalCategory c == Char.ConnectorPunctuation
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isPunctuation c = not (Char.isSpace c || isWord c)
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-- | Return Just the last index from a non-empty range, or if the range is empty, Nothing.
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maybeLastIndex :: Range -> Maybe Int
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maybeLastIndex (Range start end) | start == end = Nothing
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maybeLastIndex (Range _ end) = Just $ end - 1
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-- | Test two ranges for intersection.
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intersectsRange :: Range -> Range -> Bool
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intersectsRange range1 range2 = start range1 < end range2 && start range2 < end range1
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-- Return the (possibly empty, possibly ill-formed) intersection of two ranges.
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intersectionRange :: Range -> Range -> Range
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intersectionRange range1 range2 = Range (max (start range1) (start range2)) (min (end range1) (end range2))
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-- | Return a range that contains both the given ranges.
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unionRange :: Range -> Range -> Range
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unionRange (Range start1 end1) (Range start2 end2) = Range (min start1 start2) (max end1 end2)
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-- | Return a range that contains all the ranges in a Foldable, or the passed Range if the Foldable is empty.
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unionRangesFrom :: Foldable f => Range -> f Range -> Range
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unionRangesFrom range = maybe range sconcat . nonEmpty . toList
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-- Instances
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instance Semigroup Range where
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a <> b = unionRange a b
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instance Ord Range where
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a <= b = start a <= start b
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instance Listable Range where
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tiers = cons2 Range
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