[SOLVED] CS代考计算机代写 module Sentence where

module Sentence where

— Grammar for the animal sentence language:
—
— s::=n v n|s `and` s
— n::=`cats` | `dogs` | `ducks`
— v::=`chase` | `cuddle`

data Sentence
= NVN Noun Verb Noun
| And Sentence Sentence
deriving (Eq,Show)

data Noun = Cats | Dogs | Ducks
deriving (Eq,Show)

data Verb = Chase | Cuddle
deriving (Eq,Show)

— | The sentence: cats cuddle ducks and dogs cuddle ducks
ex1 :: Sentence
ex1 = And (NVN Cats Cuddle Ducks) (NVN Dogs Cuddle Ducks)

— | The sentence: dogs chase cats and cats chase ducks and ducks chase cats
ex2 :: Sentence
ex2 = And (NVN Dogs Chase Cats) (And (NVN Cats Chase Ducks) (NVN Ducks Chase Cats))
— ex2 = And (And (NVN Dogs Chase Cats) (NVN Cats Chase Ducks)) (NVN Ducks Chase Cats)

— | Build a sentence that is a conjunction of other sentences.
conjunction :: [Sentence] -> Maybe Sentence
conjunction []= Nothing
conjunction (h:t) = case conjunction t of
Nothing -> Just h
Just s-> Just (And h s)

— | Pretty print a sentence.
pretty :: Sentence -> String
pretty (NVN s v o) = prettyNoun s ++ ” ” ++ prettyVerb v ++ ” ” ++ prettyNoun o
pretty (And l r) = pretty l ++ ” and ” ++ pretty r

— | Pretty print a noun.
prettyNoun :: Noun -> String
prettyNoun Cats= “cats”
prettyNoun Dogs= “dogs”
prettyNoun Ducks = “ducks”

— | Pretty print a verb.
prettyVerb :: Verb -> String
prettyVerb Chase= “chase”
prettyVerb Cuddle = “cuddle”

— | Does the sentence contain only cuddling?
isNice :: Sentence -> Bool
isNice (NVN _ Chase _)= False
isNice (NVN _ Cuddle _) = True
isNice (And l r)= isNice l && isNice r