[Haskell-cafe] fromInteger for Lists
haskell at colquitt.org
Fri May 1 19:06:15 EDT 2009
> There's nothing better than making a data type an instance of Num. In
> particular, fromInteger is a joy. But how about lists?
Do you mean something like Blargh below, only useful?
dorsey at elwood:~/src/scratch$ cat list.hs
class Blargh f where
fromList :: [a] -> f a
data Foo a = Foo [a] deriving (Show)
data Bar a = Bar [a] deriving (Show)
instance Blargh Foo where
fromList = Foo
instance Blargh Bar where
fromList l = Bar (reverse l)
dorsey at elwood:~/src/scratch$ ghci list.hs
GHCi, version 6.8.3: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling Main ( list.hs, interpreted )
Ok, modules loaded: Main.
*Main> fromList [1,2,3] :: Foo Int
*Main> fromList [1,2,3] :: Bar Int
More information about the Haskell-Cafe