How would you implement a function to add elements from one slice to another if you were creating a programming language from scratch?

To implement a function that adds elements from one slice to another in a programming language from scratch, you need to consider dynamic memory management and copying elements.

Main steps:

1. Capacity check: if the current slice does not have enough capacity for new elements, a new array with increased size (usually with some margin, for example, twice as large) is allocated.
2. Copying elements: elements from the source slice are copied to the end of the target.
3. Updating slice metadata: the length of the slice is increased, and capacity is updated if necessary.

Example in pseudocode:

func appendSlice(dst, src Slice) Slice {
    totalLen := dst.len + src.len
    if totalLen > dst.cap {
        newCap := max(totalLen, dst.cap*2)
        newArray := allocateArray(newCap)
        copy(newArray, dst.array, dst.len)
        dst.array = newArray
        dst.cap = newCap
    }
    copy(dst.array[dst.len:], src.array, src.len)
    dst.len = totalLen
    return dst
}

Here, Slice is a structure with fields array (pointer to array), len (current length), and cap (capacity). The copy function copies elements from one array to another. This approach is similar to slice implementation in Go.