Useful alternative control structures?

Question

Sometimes when I am programming, I find that some particular control structure would be very useful to me, but is not directly available in my programming language. I think my

Answer 1

How about iterating with a moving window (of n elements instead of 1) through a list? This is tangentially related @munificent's answer, I think.

Something like

#python
#sum of adjacent elements
for x,y in pairs(list):
    print x + y

def pairs(l):              
    i=0                    
    while i < len(l)-1:    
        yield (l[i],l[i+1])
        i+=1               

It is useful for certain types of things. Don't get me wrong, this is easy to implement as a function, but I think a lot of people try to bring out for and while loops when there are more specific/descriptive tools for the job.