2010/7/15 Alexey Karakulov
I wonder if pattern matching could be less verbose. Maybe this sounds weird, but here is example of what I mean:
type A = (Int, String)
f :: String -> A -> A f s (i,s') = (i, s ++ s')
data B = B Int String deriving Show
g :: String -> B -> B g s (B i s') = B i $ s ++ s'
Types A/B and functions f/g are quite similar: (x :: A) or (x :: B) means that x contains some integer and string values, and f/g functions take some string and prepend it to the string part of x. The code for f and g has the same level of verbosity, but -- ta-dah! -- we can use arrows and define f in a highly laconic manner:
import Control.Arrow f' :: String -> A -> A f' = second . (++)
So my queastion is how I could define (g' :: String -> B -> B) in the same way.
I guess it is short because you make use of second... so you can define second' for your B data type, or make B an instance of Arrow. Cheers, Thu