Calendar Date Assignment

Hints and Gotchas

Hints and Gotchas credit to Charilaos Skiadas

Instructions

UW or Coursera

Code to Implement

You will write 11 SML functions (and tests for them) related to calendar dates. In all problems, a “date” is an SML value of type int*int*int, where the first part is the year, the second part is the month, and the third part is the day. A “reasonable” date has a positive year, a month between 1 and 12, and a day no greater than 31 (or less depending on the month). Your solutions need to work correctly only for reasonable dates, but do not check for reasonable dates (that is a challenge problem) and many of your functions will naturally work correctly for some/all non-reasonable dates. A “day of year” is a number from 1 to 365 where, for example, 33 represents February 2. (We ignore leap years except in one challenge problem.)

is_older

Write a function is_older that takes two dates and evaluates to true or false. It evaluates to true if the first argument is a date that comes before the second argument. (If the two dates are the same, the result is false.)

number_in_month

Write a function number_in_month that takes a list of dates and a month (i.e., an int) and returns how many dates in the list are in the given month.

number_in_months

Write a function number_in_months that takes a list of dates and a list of months (i.e., an int list) and returns the number of dates in the list of dates that are in any of the months in the list of months. Assume the list of months has no number repeated. Hint: Use your answer to the previous problem.

dates_in_month

Write a function dates_in_month that takes a list of dates and a month (i.e., an int) and returns a list holding the dates from the argument list of dates that are in the month. The returned list should contain dates in the order they were originally given.

dates_in_months

Write a function dates_in_months that takes a list of dates and a list of months (i.e., an int list) and returns a list holding the dates from the argument list of dates that are in any of the months in the list of months. Assume the list of months has no number repeated. Hint: Use your answer to the previous problem and SML’s list-append operator (@).

get_nth

Write a function get_nth that takes a list of strings and an int n and returns the nth element of the list where the head of the list is 1st. Do not worry about the case where the list has too few elements: your function may apply hd or tl to the empty list in this case, which is okay.

date_to_string

Write a function date_to_string that takes a date and returns a string of the form January 20, 2013 (for example). Use the operator ^ for concatenating strings and the library function Int.toString for converting an int to a string. For producing the month part, do not use a bunch of conditionals. Instead, use a list holding 12 strings and your answer to the previous problem. For consistency, put a comma following the day and use capitalized English month names: January, February, March, April, May, June, July, August, September, October, November, December.

number_before_reaching_sum

Write a function number_before_reaching_sum that takes an int called sum, which you can assume is positive, and an int list, which you can assume contains all positive numbers, and returns an int. You should return an int n such that the first n elements of the list add to less than sum, but the first n + 1 elements of the list add to sum or more. Assume the entire list sums to more than the passed in value; it is okay for an exception to occur if this is not the case.

what_month

Write a function what_month that takes a day of year (i.e., an int between 1 and 365) and returns what month that day is in (1 for January, 2 for February, etc.). Use a list holding 12 integers and your answer to the previous problem.

month_range

Write a function month_range that takes two days of the year day1 and day2 and returns an int list [m1,m2,...,mn] where m1 is the month of day1, m2 is the month of day1+1, ..., and mn is the month of day day2. Note the result will have length day2 - day1 + 1 or length 0 if day1>day2.

oldest

Write a function oldest that takes a list of dates and evaluates to an (int*int*int) option. It evaluates to NONE if the list has no dates and SOME d if the date d is the oldest date in the list.

number_in_months_challenge and dates_in_months_challenge

Challenge Problem: Write functions number_in_months_challenge and dates_in_months_challenge that are like your solutions to problems 3 and 5 except having a month in the second argument multiple times has no more effect than having it once. (Hint: Remove duplicates, then use previous work.)

reasonable_date

Challenge Problem: Write a function reasonable_date that takes a date and determines if it describes a real date in the common era. A “real date” has a positive year (year 0 did not exist), a month between 1 and 12, and a day appropriate for the month. Solutions should properly handle leap years. Leap years are years that are either divisible by 400 or divisible by 4 but not divisible by 100. (Do not worry about days possibly lost in the conversion to the Gregorian calendar in the Late 1500s.) Note: Remember challenge problems are not required for a high grade and will be worth (only) a few points. Note: The sample solution contains roughly 75–80 lines of code, not including challenge problems.

Syntax Hints

Small syntax errors can lead to strange error messages. Here are 3 examples for function definitions: 1. int * int * int list means int * int * (int list), not (int * int * int) list. 2. fun f x : t means the result type of f is t, whereas fun f (x:t) means the argument type of f is t. There is no need to write result types (and in later assignments, no need to write argument types). 3. fun (x t), fun (t x), or fun (t : x) are all wrong, but the error message suggests you are trying to do something much more advanced than you actually are (which is trying to write fun (x : t)).

Summary

Evaluating a correct homework solution should generate these bindings:

val is_older = fn : (int * int * int) * (int * int * int) -> bool
val number_in_month = fn : (int * int * int) list * int -> int
val number_in_months = fn : (int * int * int) list * int list -> int
val dates_in_month = fn : (int * int * int) list * int -> (int * int * int) list
val dates_in_months = fn : (int * int * int) list * int list -> (int * int * int) list
val get_nth = fn : string list * int -> string
val date_to_string = fn : int * int * int -> string
val number_before_reaching_sum = fn : int * int list -> int
val what_month = fn : int -> int
val month_range = fn : int * int -> int list
val oldest = fn : (int * int * int) list -> (int * int * int) option

Of course, generating these bindings does not guarantee that your solutions are correct.

Test

file:	unit_test_hw1.sml
source folder:	src/test/sml/hw1

Test your functions. The unit tests you have been provided are intentionally minimal.

Pledge, Acknowledgments, Citations

file:

lab-1-calendar-date-pledge-acknowledgments-citations.txt

More info about the Honor Pledge