在 Haskell 中，带有标题的程序有什么区别
module Main where
import Data.List
和
module Main where
import Data.Char
///////////////////////////////////////// /
这些是我用来学习的玩具程序：
方案一：
module Main where
import Data.Char
prepets1 = ["cat", "dog", "scorpion", "cobra"]
prepets2 = ["cat", "dog"]
prepets3 = ["cat", "scorpion"]
prepets4 = [prepets2, prepets3]
data Pet = Pet {name :: String,
venomous :: Bool,
cost :: Integer }
deriving (Eq, Show)
venomous' :: String -> Bool
venomous' = (>3). length
cost' :: String -> Integer
cost' = sum . map (fromIntegral . ord)
petify :: String -> Pet
petify s = Pet s (venomous' s) (cost' s)
pets1 = map petify prepets1
pets2 = [Pet s (venomous' s) (cost' s) | s <- prepets1]
ouch1 :: [String] -> Bool
--is any string here the name of a venomous pet?
ouch1 xs = True
ouch2 :: [[String]] -> Bool
-- Is any string here the name of a veno,ous pet?
ouch2 xs = False
printpets = putStrLn . unlines. map show
blankline = putStrLn "\n"
main = do
blankline
print $ petify "cat"
blankline
print $ petify "scorpion"
blankline
printpets pets1
blankline
printpets pets2
blankline
print $ ouch1 prepets2
blankline
print $ ouch1 prepets3
方案二：
module Main where
import Data.List
data Report = Report {recipe :: Recipe,
legal :: Bool,
popcnt :: Integer,
cost :: Integer}
deriving (Eq, Show)
type Recipe = String -- seven bits to encode seven ingredients
-- recipes in Gray-code order
gray :: Integer -> [Recipe]
gray n
| n == 0 = [""]
| n > 0 = map (++"0") (gray (n-1)) ++
map (++"1") (reverse (gray (n-1)))
recipes = gray 7
-- recipe analysis and report generation
reports = [Report r (legal' r) 6 16 | r <- recipes] -- fix!
legal_reports = [r | r <- reports, legal r]
legal' :: Recipe -> Bool
legal' r = take 3 r == "000" -- fix!
ruleset = [rule0, rule1, rule2, rule3, rule4, rule5]
-- Rule 0: If truffles, then precisely truffles.
rule0 r = True -- fix!
-- Rule 1: Either truffles or some meat.
rule1 r = False -- fix!
-- Rule 2: Not both peppers and onions.
rule2 r = True -- fix!
-- Rule 3: If bacon, then peppers.
rule3 r = False -- fix!
-- Rule 4: If sausage, then onions.
rule4 r = True -- fix!
-- Rule 5: If ham, then mushrooms.
rule5 r = False -- fix!
popcnt' :: Recipe -> Integer
-- number of ingredients
popcnt' x = 3 -- fix!
type Bit = Char
type Cost = Integer
cost' :: Recipe -> Cost
cost' x = 42 -- fix!
includeCost :: Cost -> Bit -> Cost
includeCost cost bit = if bit == '1' then cost else 0
costs = [1, 2, 4, 8, 16, 32, 64]
-- ingredient encoding
peppers r = r!!0 == '1'
bacon r = r!!1 == '1'
ham r = r!!2 == '1'
sausage r = r!!3 == '1'
onions r = r!!4 == '1'
mushrooms r = r!!5 == '1'
truffles r = r!!6 == '1'
preciselyTruffles = (== "0000001")
-- main processing
type Run = [Report] -- sequence of legal reports that satisfy the metarule
-- Approach A: Work directly with Grey-code order
runsA = extractRunsA reports
extractRunsA :: [Report] -> [Run]
extractRunsA as
| clean == [] = []
| otherwise = r : extractRunsA as'
where (r, as') = break illegal clean
clean = dropWhile illegal as
illegal = not . legal
-- Approach B: Guess a starting seed of a long Hamming run
runsB = extractRunsB legal_reports
extractRunsB :: [Report] -> [Run]
extractRunsB [] = []
extractRunsB xs = run : extractRunsB xs'
where run = buildRun (head xs) (tail xs)
xs' = xs \\ run -- list difference
buildRun :: Report -> [Report] -> Run
buildRun seed reports
| endOfRun = [seed]
| otherwise = seed : buildRun seed' reports'
where endOfRun = successors == []
successors = filter (.~. seed) reports
reports' = reports \\ [seed]
seed' = head successors
(.~.) :: Report -> Report -> Bool
-- test recipe pairs for Hamming distance 1
x .~. y = True -- fix!
-- print routines
printReports :: [Report] -> IO ()
printReports = putStrLn . unlines . map show
printRecipes :: [Report] -> IO ()
printRecipes = putStrLn . showRecipes
printRuns :: [Run] -> IO ()
printRuns = putStrLn . unlines . map showRecipes
printRuns' :: [Run] -> IO ()
printRuns' = putStrLn . unlines . map showRecipes'
showRecipes :: Run -> String
showRecipes = unlines . map showNames
showRecipes' :: Run -> String
showRecipes' run = (unlines . map showNames) run ++ " total cost = $" ++
show 15 ++ "\n" ++ -- fix!
" prize money = $" ++ show 4 ++ " million\n" -- fix!
type Name = String
showNames :: Report -> String
showNames r = (concat . addEggs . translate . recipe) r ++
" (" ++ show (popcnt r) ++ ")" ++
" $" ++ show (cost r)
translate :: Recipe -> [Name]
translate = zipWith includeName names
includeName :: Name -> Bit -> Name
includeName name bit = if bit == '1' then name else replicate (length name) ' '
addEggs :: [Name] -> [Name]
addEggs = id -- fix!
names =
["peppers ", "bacon ", "ham ", "sausage ", "onions ", "mushrooms ", "truffles"]
blankline = putStrLn ""
render = putStrLn . (++ "\n")
main = do
blankline
-- render "All reports:"
-- printReports reports
render "First ten recipes with number of ingredients and cost:"
printRecipes $ take 10 reports
render "All legal recipes with number of ingredients and cost:"
printRecipes legal_reports
render "All Gray-code runs:"
printRuns runsA
render "All Gray-code runs with total cost and prize money:"
printRuns' runsA
render "All seed-generated runs:"
printRuns runsB
render "All seed-generated runs with total cost and prize money:"
printRuns' runsB