programming language 第三周作业答案

//解法一
val only_capitals = List.filter (fn str => Char.isUpper o String.sub(str,0))
//解法二
fun only_capitals x = List.filter (fn str => Char.isUpper(String.sub(str,0)) x

fun only_capitals x = List.filter (fn str => Char.isUpper(String.sub(str,0)) x

fun longest_string1 list = List.foldl (fn (s,acc) => if String.size s > String.size acc then s else acc) "" list

val longest_string2 = List.foldl (fn (s,acc) => if String.size s< String.size acc then acc else s) ""

fun longest_string_helper f strings =
foldl (fn(x,y) => if f(String.size x, String.size y) then x else y) "" strings

val longest_string3 =
longest_string_helper (fn (x,y) => x > y)

val longest_string4 =
longest_string_helper (fn (x,y) => x >= y)

fun longest_capitalized list =( longest_string1 o only_capitals ) list

val rev_string = implode o rev o explode

fun first_answer f list =
case list of
[] => raise NoAnswer
| x::xs => case f x of
SOME v => v
| NONE => first_answer f xs

fun all_answers f list =
let
fun helper acc list =
case (acc,list) of
(_,[]) => acc
| (SOME v,x::xs) =
4000
>( case f x of
SOME xv => helper (SOME (xv @ v)) xs
| NONE => NONE)
| _ => NONE

in
helper (SOME []) list
end

val count_wildcards = g (fn () =>1) (fn x => 0)

val count_wild_and_variable_lengths = g (fn () => 1) (fn s => String.size s)

fun count_some_var (s,p) =
g (fn() => 0) (fn str => if(s = str) then 1 else 0) p

//解法一
fun check_pat p =
let
fun filterString pat acc = case pat of
Variable x => x :: acc
| ConstructorP (_, p) => filterString p acc
| TupleP ps =>
List.foldl
(fn (p, acc) => (filterString p []) @ acc) [] ps
| _ => []
in
let
val strList = filterString p []
fun checkDuplicate remList =
case remList of
[] => true
| x :: xs => if List.exists (fn item => item = x) xs
then false
else checkDuplicate xs
in
checkDuplicate strList
end
end
\\解法二
fun check_pat p =
let
fun makeList patron =
case patron of
Variable s => [s]
| TupleP ps => List.foldl (fn(i,acc) => (makeList i) @ acc) [] ps
| _ => []

fun check lista =
case lista of
[] => true
| x::xs => if((List.exists(fn y => if(x = y)
then true
else false) xs))
then
false
else
true andalso check xs
in
(check o makeList) p
end

fun match valptrn =
case valptrn
of (_, Wildcard) => SOME []
| (v, Variable s) => SOME [(s, v)]
| (Unit, UnitP) => SOME []
| (Const v, ConstP v') => if v = v' then SOME [] else NONE
| (Tuple vs, TupleP ps) =>
if length(vs) = length(ps)
then all_answers match (ListPair.zip(vs, ps))
else NONE
| (Constructor(s2, v), ConstructorP(s1, p)) =>
if s1 = s2
then match(v, p)
else NONE
| _ => NONE

fun first_match v ptrnlist =
SOME(first_answer (fn p => match(v, p)) ptrnlist)
handle NoAnswer => NONE