Question

I am new to Scheme – I am currently trying to learn the syntax and how to think recursively. I came to a section on vectors and wanted to be able to set values in my vector via some kind of looping (using recursion of course). I have this variable:

(define my-vector (make-vector 5))

which I then want to populate using the vector-set! procedure. Normally in C++ (the only other language I am really familiar with) this would be done in an iterative fashion, eg

//...

std::vector<int> myVector;

for(int i = 0; i < 5; ++i)    // populate the vector
    myVector.push_back(i);

std::vector<int>::const_iterator outIter;

for(outIter = myVector.begin();
    outIter != myVector.end(); ++outIter)
    std::cout << *outIter << " ";

std::cout << std::endl;

//...

However, I know that this kind of thing should be done via recursion in Scheme. What would a recursive populate-vector procedure might look like??

Answer 1

(let f ((i 0))
  (when (< i 5)
    (vector-set! my-vector i i)
    (f (+ i 1))))

You can try it online here.

You can also try using the DO syntax, but most find it hard to remember 🙂

Learning to use named LET is very important.

Also note, a Scheme vector is just a fixed-sized array.