在 haskell 中生成给定月份和年份的日历

Question

一周以来我一直在学习haskell并且面临着不同的问题。这次我必须根据给定的月份和年份创建一个日历。我快完成了，但问题是我无法从开始的那一天开始填充日子。

我的解决方案是

getDaysInMonth year month=(nDays,sDay) 
                          where nDays = gregorianMonthLength year month
                                sDay= digitToInt(last(showWeekDate (fromGregorian year month 01)))
year=2013
month=10
months=["JANUARY","FEBRUARY","MARCH","APRIL","MAY","JUNE","JULY","AUGUST","SEPTEMBER","OCTOBER","NOVEMBER","DECEMBER"]
mnth=months!!(month-1)
monthDate = getDaysInMonth year month
startAt=snd(monthDate)
totalDays = fst(monthDate)
printLine = "\n"++concat ["+---\t" | r <- [1..7]]
check x | x>totalDays=""
        | x<=totalDays=show x
genDays n m="\n "++concat[check(x)++"\t|"|x<-[n..m]]
genD 6=""
genD sP=genDays ((sP-1)*7+1) (sP*7) ++genD (sP+1)
generateCalendar=printLine++"\n "++
                        concat [[r]++"\t|" | r <- mnth]++printLine++
                        "\n Sun\t|Mon\t|Tue\t|Wed\t|Thu\t|Fri\t|Sat"++printLine++
                        genD 1
main=do
     putStrLn generateCalendar

这个程序的输出是这样的

+---+---+---+---+---+---+---    
 O  |C  |T  |O  |B  |E  |R  |
+---+---+---+---+---+---+---    
 Sun|Mon|Tue|Wed|Thu|Fri|Sat
+---+---+---+---+---+---+---    
 1  |2  |3  |4  |5  |6  |7  |
 8  |9  |10 |11 |12 |13 |14 |
 15 |16 |17 |18 |19 |20 |21 |
 22 |23 |24 |25 |26 |27 |28 |
 29 |30 |31 |   |   |   |   |

所以问题是 10 月份应该从星期一开始。我认为解决方案的实施有点混乱，但我该如何解决这个问题？

提前致谢

Answer 1

解决此问题的更 "functional" 方法是：

创建一个包含 35 个字符串的列表，每个字符串要么是空字符串，要么是一个（字符串化的）数字。
将列表分成多个块，每个块包含 7 个元素（因此您得到五个块）
对于每个块，将元素呈现为日历中的一行。

例如，对于 2013 年 10 月，35 个字符串的列表为：

cells = [ "", "", "", "1", "2", "3", ..., "31", "", "" ]

可以使用这个辅助函数创建块：

chunksOf7 (a:b:c:d:e:f:g:rest) = [ [a,b,c,d,e,f,g] ] ++ chunksOf7 rest
chunksOf7 xs = xs

（有更好的方法来定义 chunksOf7，但这就足够了。）

并渲染块：

renderChunk cells =  (concat $ map renderCell cells) ++ "\n"
renderCell c = pad 3 c ++ "|"
pad n str = str ++ (replicate (n-(length str)) ' ')

pad n str 在字符串 str 的右边用空格填充，直到总长度为 n。 replicate n a 创建一个值 a 重复 n 次的列表。

并将它们放在一起（一旦你有了 cells 列表）：

renderCalendarBody cells =  concat (map renderChunk chunks)
  where chunks = chunksOf7 cells

现在，给定一年零一个月，您只需编写一个函数来定义 cells 是什么。单元格列表将包括：

一些前导空字符串
后跟 1 到 30（或 31 或任何月份的最后一天）
后跟一些尾随空字符串

即：

cellsForYearAndMonth y m = (replicate n1 "")
                              ++ [ show d | d <- [1..lastday] ]
                              ++ (replicate n2 "")
  where lastday = ...
        n1 = ... number of leading empty strings ...
        n2 = ... number of trailing empty strings ...

Answer 2

谢谢@user5402。终于我得到了工作版本

import Data.Time.Calendar
import Data.Time.Calendar.WeekDate
import Data.Char
year=2014
month=2
months=["JANUARY","FEBRUARY","MARCH","APRIL","MAY","JUNE","JULY","AUGUST","SEPTEMBER","OCTOBER","NOVEMBER","DECEMBER"]
mnth=months!!(month-1)
monthDate = getDaysInMonth year month
startAt=snd(monthDate)
totalDays = fst(monthDate)

getDaysInMonth year month=(nDays,sDay) 
                      where nDays = gregorianMonthLength year month
                            sDay= digitToInt(last(showWeekDate (fromGregorian year month 01)))
cells = (replicate n1 "")
                          ++ [ show d | d <- [1..lastday] ]
                          ++ (replicate n2 "")
          where lastday = totalDays
                n1=(startAt-1)
                n2=(7-(totalDays-(29-startAt)))
chunksOf7 []=[]
chunksOf7 (a:b:c:d:e:f:g:rest) = [ [a,b,c,d,e,f,g] ] ++ chunksOf7 rest

pad n str = str ++ (replicate (n-(length str)) ' ')
renderCell c = pad 3 c ++ "|"
renderChunk cells =  (concat $ map renderCell cells) ++ "\n"

printLine = "\n"++concat ["+---" | r <- [1..7]]++"\n"
monthLine=concat [[r]++" |" | r <- mnth]
dayLine="Sun|Mon|Tue|Wed|Thu|Fri|Sat"
heading=concat[printLine,"Year: ",show year,printLine,monthLine,printLine,dayLine,printLine]

renderCalendarBody cells =  heading++concat (map renderChunk chunks)
  where chunks = chunksOf7 cells

main= do putStrLn $ renderCalendarBody cells

在 haskell 中生成给定月份和年份的日历

generate calendar of a given month and year in haskell

haskell

functional-programming