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Last Friday of each month: Difference between revisions
adding Elm solution
(→{{header|Ruby}}: removed require rubygems) |
(adding Elm solution) |
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2012-11-30
2012-12-28
</pre>
=={{header|Elm}}==
<lang elm>import Html exposing (Html, Attribute, text, div, input)
import Html.Attributes exposing (placeholder, value, style)
import Html.Events exposing (on, targetValue)
import Signal exposing (Address)
import StartApp.Simple exposing (start)
import String exposing (toInt)
import Maybe exposing (withDefault)
import List exposing (map, map2)
import List.Extra exposing (scanl1)
lastFridays : Int -> List Int
lastFridays year =
let isLeap = (year % 400) == 0 || ( (year % 4) == 0 && (year % 100) /= 0 )
daysInMonth = [31, if isLeap then 29 else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
y = year-1
in scanl1 (+) daysInMonth
|> map2 (\len day -> len - (day + 2 + y + y//4 - y//100 + y//400) % 7) daysInMonth
lastFridayStrings : String -> List String
lastFridayStrings yearString =
let months= ["January ", "February ", "March ", "April ", "May ", "June ", "July ", "August ", "September ", "October ", "November ", "December "]
errString = "Only years after 1752 are valid."
in case toInt yearString of
Ok year ->
if (year < 1753)
then [errString]
else lastFridays year
|> map2 (\m d -> m ++ toString d ++ ", " ++ toString year) months
Err _ ->
[errString]
main = start { model = "", view = view, update = update }
update newStr oldStr = newStr
view : Address String -> String -> Html
view address yearString =
div []
([ input
[ placeholder "Enter a year."
, value yearString
, on "input" targetValue (Signal.message address)
, myStyle
]
[]
] ++ (lastFridayStrings yearString
|> map (\date -> div [ myStyle ] [ text date ]) ))
myStyle : Attribute
myStyle =
style
[ ("width", "100%")
, ("height", "20px")
, ("padding", "5px 0 0 5px")
, ("font-size", "1em")
, ("text-align", "left")
]</lang>
Sample run for the year 2003; copied and pasted from web-page:
{{out}}
<pre>January 31, 2003
February 28, 2003
March 28, 2003
April 25, 2003
May 30, 2003
June 27, 2003
July 25, 2003
August 29, 2003
September 26, 2003
October 31, 2003
November 28, 2003
December 26, 2003
</pre>
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