(* CS 312 Problem Set 1 solutions *)

(* Part 1: Post to cornell.test *)


(***************************************************************************)
(* Part 2: Style improvement *)

(* a *)
(* 
 * If count is positive, append count dashes and a star to the base string.
 * Otherwise, append only a star.
 *)
fun foo(count:int, base:string):string =
  if (count <= 0) then base ^ "*"
  else foo(count - 1, base ^ "-")

(* b *)
fun partB (p:bool, q:bool):bool =
  not p orelse q

(* c *)
fun fib (x:int):int = 
  case x of
    0 => 1
  | 1 => 1
  | _ => fib (x-1) + fib (x-2)

(* d *)
fun printFibs (x:int):unit =
  let
    val n    = Int.toString x
    val fibN = Int.toString (fib x)
  in
    print ("The Fibonacci number at position " ^ n ^ " is " ^ fibN ^ ".\n"
	   ^ fibN ^ " is my favorite number.  Is " ^ fibN
	   ^ " your favorite number too?")
  end


(***************************************************************************)
(* Part 3: `val' and `fun' declarations *)

(* a *)
val reallyCoolPeople = ("Ramin", "Tibor", "Siggi", "Hubert", "Abhishek",
			"Jackie", "Saikat", "Frances", "Kori", "Jeff",
			"Justin", "Tim", "Serge", "H", "Greg", "Jeff",
			"Walter", "Emmanuel")

(* b *)
val lastLetter = #"e"

(* c *)
val personal = {name="J. Random Hacker", age=42, cs=true}

(* d *)
fun cookingConversions (from:string, num:real, to:string):real =
  num * (case (from, to) of
	   ("CUPS", "QUARTS")   => 0.25000000
	 | ("CUPS", "LITERS")   => 0.23658823
	 | ("QUARTS", "CUPS")   => 4.00000000
	 | ("QUARTS", "LITERS") => 0.94635295
	 | ("LITERS", "CUPS")   => 4.22675280
	 | ("LITERS", "QUARTS") => 1.05668820
	 | _                    => 1.00000000)

(* e *)
fun gcd (j:int, k:int):int =
  case (j,k) of 
      (0, _) => k
    | (_, 0) => j
    |    _   => 
           if (j = k) then j else 
             case (j mod 2, k mod 2) of
                (0,0) => 2 * (gcd (j div 2, k div 2))
              | (0,1) => gcd (j div 2, k)
              | (1,0) => gcd (j, k div 2)
              | _     => if j < k then gcd (k div 2 - j div 2, j)
                         else gcd (k, j)


(***************************************************************************)
(* Part 4: The Standard Basis Library is your friend *)

(* a *)
fun isFifthCharUpper (s:string):bool =
  (String.size s >= 5) andalso (Char.isUpper (String.sub (s, 4)))

(* b *)
fun extractIntAndFraction (r:real):int*real =
  let
    val {whole=i, frac=f} = Real.split r
  in
    (Real.round i, f)
  end

(* c *)
fun currentTimeString ():string =
  Date.toString (Date.fromTimeLocal (Time.now ()))