Thanks you 

On Tuesday, January 2, 2018 at 6:09:23 PM UTC, gneuner2 wrote:
>
> On 1/2/2018 12:43 PM, Sanjeeb Sinkhada wrote: 
> > hi could anyone help me with this question? 
> > Write a function that will take a list of pairs and return just the 
> > pair comprising the first element of the first pair and the second 
> > element of the last pair. 
> >  Eg. 
> >  > (reduce-pairs ’()) 
> > NIL 
> >  > (reduce-pairs ’((1 2) (3 4))) 
> > (1 4) 
> >  > (reduce-pairs ’((1 2) (3 4) (5 6))) 
> > (1 6) 
> > 
> > I have got this so far 
> > (define reduce-pair(λ(x y)(cond 
> >                           ((pair? x)x) 
> >                           (cons( car x) 
> >                                (cons ( list-tail (second y))))))) 
> > but its completely wrong 
> > thanks in advance 
>
> Yup, it definitely is wrong.  <grin>   This smells like homework and the 
> homework policy in this forum is to help but not answer directly. 
>
>
> First, your examples have a single list argument, but your function is 
> defined to have 2 arguments.  Why? 
> Second, what should happen if the list contains only 1 pair or contains 
> elements that are not pairs? 
> Third, are you supposed to solve the problem by walking the list, or can 
> you use any pre-defined list functions? 
>
> Think about how you would get the first and last elements of the list.  
> Then think about how you get the first and second values of those 
> pairs.  Then think about how to make a new pair from those values.   If 
> you can use any predefined function, then you're at least half way there 
> already ... you just need to put it together. 
>
> George 
>

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