SCIP in C++11 ― 2.2.1節 その1

2.2.1節　並びの表現：問題2.17～2.18

tuple使ってた頃はcdrの実装でえらい苦労した部分。

Compositeパターンとshared_ptrを使ったListに変えてすっきり。

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// list-ref

const List listRef(const List& listIn, const int nthElement)

{

    if(0==nthElement){return(car(listIn));}

    return(listRef(cdr(listIn),nthElement-1));

}

//concatenate lists

const List append(const List& listIn1,

                  const List& listIn2)

{

    if(isNull(listIn1)){return(makeCopyList(listIn2));}

    return(cons(car(listIn1),append(cdr(listIn1),listIn2)));

}

// final element of a list

const List lastPair(const List& listIn)

{return(listRef(listIn,length(listIn)-1));}

// reverse list

const List reverse(const List& listIn)

{

    if(isNull(listIn)){return(makeList());}

    return(append(reverse(cdr(listIn)),makeList(car(listIn))));

}

//---------abstraction barrier---------

int main(int argc, char** argv)

{

    auto oneThroughFour(makeList(1,2,3,4));

   

    cout<<"one-through-four="

        <<listString(oneThroughFour)<<endl;

    cout<<"(car one-thgough-four)="

        <<value<int>(car(oneThroughFour))<<endl;

    cout<<"(cdr one-through-four)="

        <<listString(cdr(oneThroughFour))<<endl;

    cout<<"(car (cdr one-through-four))="

        <<value<int>(cadr(oneThroughFour))<<endl;

    cout<<"(cons 10 one-through-four)="

        <<listString(cons(10,oneThroughFour))<<endl;

    cout<<"(cons 5 one-through-four)="

        <<listString(cons(5,oneThroughFour))<<endl;

    auto squares(makeList(1,4,9,16));

    cout<<"squares="<<listString(squares)<<endl;

    cout<<"(list-ref squares 3)="<<value<int>(listRef(squares,3))<<endl;

    auto odds(makeList(1,3,5,7));

    cout<<"odds="<<listString(odds)<<endl;

    cout<<"(length odds)="<<length(odds)<<endl;

    cout<<"(append squares odds)="

        <<listString(append(squares,odds))<<endl;

    cout<<"(append odds squares)="

        <<listString(append(odds,squares))<<endl;

    cout<<endl<<"Excersize 2.17:"<<endl;

    auto list1(makeList(23,72,149,34));

    cout<<"list1="<<listString(list1)<<endl;

    cout<<"(last-pair list1)="<<value<int>(lastPair(list1))<<endl;

   

    cout<<endl<<"Excersize 2.18:"<<endl;

    auto square2(makeList(1,4,9,16,25));

    cout<<"square2="<<listString(square2)<<endl;

    cout<<"(reverse square2)="<<listString(reverse(square2))<<endl;

}

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出力

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one-through-four=(1 2 3 4)

(car one-thgough-four)=1

(cdr one-through-four)=(2 3 4)

(car (cdr one-through-four))=2

(cons 10 one-through-four)=(10 1 2 3 4)

(cons 5 one-through-four)=(5 1 2 3 4)

squares=(1 4 9 16)

(list-ref squares 3)=16

odds=(1 3 5 7)

(length odds)=4

(append squares odds)=(1 4 9 16 1 3 5 7)

(append odds squares)=(1 3 5 7 1 4 9 16)

Excersize 2.17:

list1=(23 72 149 34)

(last-pair list1)=34

Excersize 2.18:

square2=(1 4 9 16 25)

(reverse square2)=(25 16 9 4 1)