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
