diff options
| -rw-r--r-- | libraries/base/GHC/Enum.hs | 46 |
1 files changed, 42 insertions, 4 deletions
diff --git a/libraries/base/GHC/Enum.hs b/libraries/base/GHC/Enum.hs index 234ccb3ba2..af74f7c984 100644 --- a/libraries/base/GHC/Enum.hs +++ b/libraries/base/GHC/Enum.hs @@ -92,13 +92,51 @@ class Enum a where -- applied to a value that is too large to fit in an 'Int'. fromEnum :: a -> Int - -- | Used in Haskell's translation of @[n..]@. + -- | Used in Haskell's translation of @[n..]@ with @[n..] = enumFrom n@, + -- a possible implementation being @enumFrom n = n : enumFrom (succ n)@. + -- For example: + -- + -- * @enumFrom 4 :: [Integer] = [4,5,6,7,...]@ + -- * @enumFrom 6 :: [Int] = [6,7,8,9,...,maxBound :: Int]@ enumFrom :: a -> [a] - -- | Used in Haskell's translation of @[n,n'..]@. + -- | Used in Haskell's translation of @[n,n'..]@ + -- with @[n,n'..] = enumFromThen n n'@, a possible implementation being + -- @enumFromThen n n' = n : n' : worker (f x) (f x n')@, + -- @worker s v = v : worker s (s v)@, @x = fromEnum n' - fromEnum n@ and + -- @f n y + -- | n > 0 = f (n - 1) (succ y) + -- | n < 0 = f (n + 1) (pred y) + -- | otherwise = y@ + -- For example: + -- + -- * @enumFromThen 4 6 :: [Integer] = [4,6,8,10...]@ + -- * @enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound :: Int]@ enumFromThen :: a -> a -> [a] - -- | Used in Haskell's translation of @[n..m]@. + -- | Used in Haskell's translation of @[n..m]@ with + -- @[n..m] = enumFromTo n m@, a possible implementation being + -- @enumFromTo n m + -- | n <= m = n : enumFromTo (succ n) m + -- | otherwise = []@. + -- For example: + -- + -- * @enumFromTo 6 10 :: [Int] = [6,7,8,9,10]@ + -- * @enumFromTo 42 1 :: [Integer] = []@ enumFromTo :: a -> a -> [a] - -- | Used in Haskell's translation of @[n,n'..m]@. + -- | Used in Haskell's translation of @[n,n'..m]@ with + -- @[n,n'..m] = enumFromThenTo n n' m@, a possible implementation + -- being @enumFromThenTo n n' m = worker (f x) (c x) n m@, + -- @x = fromEnum n' - fromEnum n@, @c x = bool (>=) (<=) (x > 0)@ + -- @f n y + -- | n > 0 = f (n - 1) (succ y) + -- | n < 0 = f (n + 1) (pred y) + -- | otherwise = y@ and + -- @worker s c v m + -- | c v m = v : worker s c (s v) m + -- | otherwise = []@ + -- For example: + -- + -- * @enumFromThenTo 4 2 -6 :: [Integer] = [4,2,0,-2,-4,-6]@ + -- * @enumFromThenTo 6 8 2 :: [Int] = []@ enumFromThenTo :: a -> a -> a -> [a] succ = toEnum . (+ 1) . fromEnum |