On Wed, 2005-07-20 at 17:06 +0100, Andy Gimblett wrote:
A small stylistic question: what's the "best" way to build strings containing other values? For example, I have:
data Process = Stop | Prefix String Process | External Process Process
instance Show Process where show Stop = "Stop" show (Prefix l p) = "(" ++ l ++ "->" ++ show p ++ ")" show (External p q) = "(" ++ show p ++ " [] " ++ show q ++ ")"
but to me the extensive use of ++ is not particularly readable.
It is also inefficient because append has complexity proportional to the length of its left argument. That's why the Prelude defines: type ShowS = String -> String and functions like showsPrec, shows, showChar
Is there a facility like this in Haskell? Or something else I should be using, other than lots of ++ ?
It looks to me like you are doing some kind of pretty printing - that is you are not printing the term using Haskell syntax. My preference is to only use Show where it is derived from the data declaration, and use a hand-written pretty printer for other tasks, for example Text.PrettyPrint Cheers, Bernie.