G; assign(L, index, val): Returns a new list identical to L, but in which the item at the index position in L is replaced by val.

# Thinking approach: Don't see an obvious base case. So, probably not a recursive solution
# Think of another way. Slicing is available to us. May be make use of that. Chop into
# three parts: items before the value, the value to be replaced, and the items after. 

#  replace the middle part with the new value, and reassemble the three parts. To

# reassemble, make use of the concat function that we already wrote.

def assign(L, index, val):
    if (len(L) > index+1):
        return concat(L[0..index].append(val),  L[index+1:])
    elif (len(L) == index+1):
        return L[0..index].append(val)
    else:
        return "error"

# You can try doing this without indexing operation availability.