Homework 3

(* Coursera Programming Languages, Homework 3, Provided Code *)

exception NoAnswer

datatype pattern = Wildcard | Variable of string | UnitP | ConstP of int | TupleP of pattern list | ConstructorP of string * pattern

datatype valu = Const of int | Unit | Tuple of valu list | Constructor of string * valu

fun g f1 f2 p = let val r = g f1 f2 in case p of Wildcard => f1 () | Variable x => f2 x | TupleP ps => List.foldl (fn (p,i) => (r p) + i) 0 ps | ConstructorP(_,p) => r p | _ => 0 end

(**** for the challenge problem only ****)

datatype typ = Anything | UnitT | IntT | TupleT of typ list | Datatype of string

(**** you can put all your code here ****)

(* 1 *) fun only_capitals (xs) = List.filter (fn(s)=>Char.isUpper(String.sub(s,0))) xs;

(* 2 *) fun longest_string1 (xs) = foldl (fn(x,y) => if String.size(x)>String.size(y) then x else y) "" xs;

(* 3 *) fun longest_string2 (xs) = foldl (fn(x,y) => if String.size(x)>=String.size(y) then x else y) "" xs;

(* 4 *) fun longest_string_helper (f:int*int->bool) (xs:string list) = foldl (fn(x,y) => if f(String.size(x),String.size(y)) then x else y) "" xs; val longest_string3 = longest_string_helper (fn(x,y) => x>y); val longest_string4 = longest_string_helper (fn(x,y) => x>=y);

(* 5 *) val longest_capitalized = longest_string1 o only_capitals;

(* 6 *) val rev_string = String.implode o List.rev o String.explode;

(* 7 *) fun first_answer f [] = raise NoAnswer | first_answer f (x::xs) = case f(x) of NONE => first_answer f xs | SOME v => v;
(* 8 *) fun all_answers f xs = let fun aux ([],acc) = SOME acc | aux (x::xs,acc) = case f(x) of NONE => NONE | SOME v =>