[Haskell-beginners] Re: how to define a user datatype consisting of instances of String?

23 Oct 2008


      On Thu, 23 Oct 2008 15:07:09 +0900, Benjamin L.Russell
 wrote:
...
module Wine where
data Wine = Red | White
data Red = "Merlot"
data White = "Sauvignon Blanc"
data Entree = "pork" | "chicken" | "tuna"
data SideDish = "garlic bread" | "mozzarella sticks" | "caviar"
wine :: [Entree] -> [SideDish] -> [(Entree, SideDish, Wine)]
wine entree sidedish
   | entree == "pork" = 
       | sidedish == "garlic bread" = ("pork", "garlic bread",
"Merlot")
       | sidedish == "mozzarella sticks" = ("pork", "mozzarella
sticks", "Merlot")
       | sidedish == "caviar" = ("pork", "caviar", "Sauvignon Blanc")
   | entree == "chicken" = 
       | sidedish == "garlic bread" = ("chicken", "garlic bread",
"Merlot")
       | sidedish == "mozzarella sticks" = ("chicken", "mozzarella
sticks", "Sauvignon Blanc")
       | sidedish == "caviar"= ("chicken", "caviar", "Merlot")
   | entree == "tuna" = 
       | sidedish == "garlic bread" = ("tuna", "garlic bread",
"Sauvignon Blanc")
       | sidedish == "mozzarella sticks" = ("tuna", "mozzarella
sticks", "Merlot")
       | sidedish == "caviar"= ("tuna", "caviar", "Merlot")
Sorry, I forgot to take care of list comprehension.  I'm not quite
sure how to extract elements of both lists at the same time in a
nested guard.  Here's a slight revision; would this work?
	
module Wine where 
    
data Wine = Red | White
data Red = "Merlot"
data White = "Sauvignon Blanc"
data Entree = "pork" | "chicken" | "tuna"
data SideDish = "garlic bread" | "mozzarella sticks" | "caviar"

wine :: [Entree] -> [SideDish] -> [(Entree, SideDish, Wine)]
wine entrees sidedishes
    | entree <- entrees == "pork" = 
        | sidedish <- sidedieshes == "garlic bread" = ("pork", "garlic
bread",
"Merlot")
        | sidedish <- sidedishes == "mozzarella sticks" = ("pork",
"mozzarella
sticks", "Merlot")
        | sidedish <- sidedishes == "caviar" = ("pork", "caviar",
"Sauvignon Blanc")
    | entree <- entrees == "chicken" = 
        | sidedish <- sidedieshes == "garlic bread" = ("chicken",
"garlic bread",
"Merlot")
        | sidedish <- sidedieshes == "mozzarella sticks" = ("chicken",
"mozzarella
sticks", "Sauvignon Blanc")
        | sidedish <- sidedieshes == "caviar"= ("chicken", "caviar",
"Merlot")
    | entree <- entrees == "tuna" = 
        | sidedish <- sidedieshes == "garlic bread" = ("tuna", "garlic
bread",
"Sauvignon Blanc")
        | sidedish <- sidedieshes == "mozzarella sticks" = ("tuna",
"mozzarella
sticks", "Merlot")
        | sidedish <- sidedieshes == "caviar"= ("tuna", "caviar",
"Merlot")

-- Benjamin L. Russell