华盛顿大学程序设计语言第4周作业答案

最新推荐文章于 2022-08-13 13:29:24 发布

原创最新推荐文章于 2022-08-13 13:29:24 发布 · 503 阅读

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#作业答案 #程序设计语言

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本文介绍了一个函数式编程的实践案例，包括数据类型定义、模式匹配、递归函数等核心概念的应用。通过对具体问题的解决过程，展示了函数式编程在处理复杂逻辑时的优势。

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顺序不对，见谅。这次作业挺难，最后也只得了80分，我就对着答案改了一下。挑战作业依旧不会，标准答案也没给出。

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
fun check_pat p=
    let fun helper1 p=case p of Variable x =>[x]
                  | TupleP ps =>List.foldl(fn(p,i)=>i@(helper1 p)) [] ps
                  | ConstructorP(_,p)=>helper1 p
                  | _ =>[]
    fun helper2 lst=case lst of []=>true
                  | x::xs =>(not(List.exists (fn y=>x=y) xs)) andalso helper2(xs)
    in (helper2 o helper1) p
    end
datatype typ = Anything
         | UnitT
         | IntT
         | TupleT of typ list
         | Datatype of string


fun count_some_var(str,p)=g (fn()=>0) (fn x=>if(x=str)then 1 else 0) p
fun count_wild_and_variable_lengths p=g (fn()=>1) String.size p
fun count_wildcards p=g (fn ()=>1) (fn _=>0) p
fun only_capitals strs=List.filter (Char.isUpper o (fn str=>String.sub(str,0))) strs
fun longest_string1 strs=foldl (fn (str,str0)=>if String.size str>String.size str0 then str else str0) "" strs                 
fun longest_string2 strs=foldl (fn (str,str0)=>if String.size str>=String.size str0 then str else str0) "" strs
fun longest_string_helper f=fn strs=>foldl (fn (str,str0)=>if f(str,str0) then str else str0) "" strs
val longest_string3=longest_string_helper (fn (str,str0)=>String.size str>String.size str0)
val longest_string4=longest_string_helper (fn (str,str0)=>String.size str>=String.size str0)
val longest_capitalized=longest_string1 o only_capitals
val rev_string =String.implode o List.rev o String.explode
fun first_answer f=fn lst=>case lst of
                   []=>raise NoAnswer
                 | x::xs =>case f(x) of
                      SOME v=>v
                    | NONE =>first_answer f xs
fun all_answers f lst=
    case lst of
    []=>SOME []
      | x::xs =>(case f(x) of SOME v=>(case all_answers f xs of NONE=>NONE
                              | SOME i =>SOME(v@i))
                | NONE =>NONE)
fun another_all_answers f lst=
    let fun helper(acc,xs)=
        case xs of
        []=>SOME acc
          | x::xs' =>case f x of
                 NONE=>NONE
               | SOME v =>helper((acc@v),xs')
    in
    helper([],lst)
    end
fun match(v,p)=case(v,p) of (_,Wildcard)=>SOME []
            | (_,Variable s) =>SOME [(s,v)]
            | (Unit,UnitP) =>SOME []
            | (Const a,ConstP b) =>if a=b 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 ps=SOME(first_answer(fn p=>match(v,p)) ps)
             handle NoAnswer=>NONE