Concatenate two lists in Common Lisp












2















I set myself to the task to write a Common Lisp function that concatenates two lists without using append.



Common Lisp input (concat-lists '(1 2 3) '(4 5 6)) should return (1 2 3 4 5 6)



Even though my solution seems to work it looks overtly complicated



(defun concat-lists(seq1 seq2)

    (cond ((not (null seq1)) (cons (car seq1) (concat-lists (cdr seq1) seq2)))

          (T (cond ((not (null seq2)) (cons (car seq2) (concat-lists seq1 (cdr seq2))))

                   (T nil)))))


What I'm looking for is a more elegant solution using reduce where I use seq1 as initial value and then apply a function to each element of seq2, thereby appending each value of the list to seq1. Somehow I always get stuck when trying....



Any help or input is much appreciated. Thanks!






lisp common-lisp







share|improve this question





























    2















    I set myself to the task to write a Common Lisp function that concatenates two lists without using append.



    Common Lisp input (concat-lists '(1 2 3) '(4 5 6)) should return (1 2 3 4 5 6)



    Even though my solution seems to work it looks overtly complicated



    (defun concat-lists(seq1 seq2)
    
    (cond ((not (null seq1)) (cons (car seq1) (concat-lists (cdr seq1) seq2)))
    
          (T (cond ((not (null seq2)) (cons (car seq2) (concat-lists seq1 (cdr seq2))))
    
                   (T nil)))))


    What I'm looking for is a more elegant solution using reduce where I use seq1 as initial value and then apply a function to each element of seq2, thereby appending each value of the list to seq1. Somehow I always get stuck when trying....



    Any help or input is much appreciated. Thanks!






    lisp common-lisp







    share|improve this question



























      2












      2








      2








      I set myself to the task to write a Common Lisp function that concatenates two lists without using append.



      Common Lisp input (concat-lists '(1 2 3) '(4 5 6)) should return (1 2 3 4 5 6)



      Even though my solution seems to work it looks overtly complicated



      (defun concat-lists(seq1 seq2)
      
    (cond ((not (null seq1)) (cons (car seq1) (concat-lists (cdr seq1) seq2)))
      
          (T (cond ((not (null seq2)) (cons (car seq2) (concat-lists seq1 (cdr seq2))))
      
                   (T nil)))))


      What I'm looking for is a more elegant solution using reduce where I use seq1 as initial value and then apply a function to each element of seq2, thereby appending each value of the list to seq1. Somehow I always get stuck when trying....



      Any help or input is much appreciated. Thanks!






      lisp common-lisp







      share|improve this question
















      I set myself to the task to write a Common Lisp function that concatenates two lists without using append.



      Common Lisp input (concat-lists '(1 2 3) '(4 5 6)) should return (1 2 3 4 5 6)



      Even though my solution seems to work it looks overtly complicated



      (defun concat-lists(seq1 seq2)
      
    (cond ((not (null seq1)) (cons (car seq1) (concat-lists (cdr seq1) seq2)))
      
          (T (cond ((not (null seq2)) (cons (car seq2) (concat-lists seq1 (cdr seq2))))
      
                   (T nil)))))


      What I'm looking for is a more elegant solution using reduce where I use seq1 as initial value and then apply a function to each element of seq2, thereby appending each value of the list to seq1. Somehow I always get stuck when trying....



      Any help or input is much appreciated. Thanks!






      lisp common-lisp




      lisp common-lisp






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Nov 20 '18 at 23:39









      Rainer Joswig

      111k8169286




      111k8169286










      asked Nov 20 '18 at 22:51









      lawrence313lawrence313

      177




      177
























          3 Answers
          3






          active

          oldest

          votes


















          4














          CL-USER 39 > (reduce #'cons
          
                     '(1 2 3 4 5)
          
                     :initial-value '(a b c d e)
          
                     :from-end t) 
          
(1 2 3 4 5 A B C D E)





          share|improve this answer
























          • seems so obvious now... thanks!

            – lawrence313
            Nov 21 '18 at 0:15



















          4














          The solution of Rainer Joswig is really elegant and simple, and respects your request of using reduce.



          If you want to see also a recursive, simple solution, then here is the classical one:



          (defun concat-lists (seq1 seq2)
          
  (if (null seq1)
          
      seq2
          
      (cons (car seq1) (concat-lists (cdr seq1) seq2))))
          

          
(concat-lists '(1 2 3) '(4 5 6))
          
(1 2 3 4 5 6)





          share|improve this answer

































            2














            I do understand your requirement for 'reduce'. and here other options:



            CL also has 'concatenante'



            (concatenate 'list '(1 2 3) '(4 5 6))



            There is also the other less complicated (IMHO), and not as elegant.



            (defun concat-lists (list1 list2)
            (let ((a (copy-list list1))
            (b (copy-list list2)))
            (rplacd (last a) b)
            a))



            or



            (defun concat-lists (list1 list2)
            (let ((a (copy-list list1))
            (b (copy-list list2)))
            (nconc a b)))






            share|improve this answer





















            • 1





              There is no need to copy list2 in both your functions, since it will not be modified.

              – Renzo
              Nov 25 '18 at 10:27











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            3 Answers
            3






            active

            oldest

            votes








            3 Answers
            3






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            4














            CL-USER 39 > (reduce #'cons
            
                     '(1 2 3 4 5)
            
                     :initial-value '(a b c d e)
            
                     :from-end t) 
            
(1 2 3 4 5 A B C D E)





            share|improve this answer
























            • seems so obvious now... thanks!

              – lawrence313
              Nov 21 '18 at 0:15
















            4














            CL-USER 39 > (reduce #'cons
            
                     '(1 2 3 4 5)
            
                     :initial-value '(a b c d e)
            
                     :from-end t) 
            
(1 2 3 4 5 A B C D E)





            share|improve this answer
























            • seems so obvious now... thanks!

              – lawrence313
              Nov 21 '18 at 0:15














            4












            4








            4







            CL-USER 39 > (reduce #'cons
            
                     '(1 2 3 4 5)
            
                     :initial-value '(a b c d e)
            
                     :from-end t) 
            
(1 2 3 4 5 A B C D E)





            share|improve this answer













            CL-USER 39 > (reduce #'cons
            
                     '(1 2 3 4 5)
            
                     :initial-value '(a b c d e)
            
                     :from-end t) 
            
(1 2 3 4 5 A B C D E)






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered Nov 20 '18 at 23:46









            Rainer JoswigRainer Joswig

            111k8169286




            111k8169286













            • seems so obvious now... thanks!

              – lawrence313
              Nov 21 '18 at 0:15



















            • seems so obvious now... thanks!

              – lawrence313
              Nov 21 '18 at 0:15

















            seems so obvious now... thanks!

            – lawrence313
            Nov 21 '18 at 0:15





            seems so obvious now... thanks!

            – lawrence313
            Nov 21 '18 at 0:15













            4














            The solution of Rainer Joswig is really elegant and simple, and respects your request of using reduce.



            If you want to see also a recursive, simple solution, then here is the classical one:



            (defun concat-lists (seq1 seq2)
            
  (if (null seq1)
            
      seq2
            
      (cons (car seq1) (concat-lists (cdr seq1) seq2))))
            

            
(concat-lists '(1 2 3) '(4 5 6))
            
(1 2 3 4 5 6)





            share|improve this answer






























              4














              The solution of Rainer Joswig is really elegant and simple, and respects your request of using reduce.



              If you want to see also a recursive, simple solution, then here is the classical one:



              (defun concat-lists (seq1 seq2)
              
  (if (null seq1)
              
      seq2
              
      (cons (car seq1) (concat-lists (cdr seq1) seq2))))
              

              
(concat-lists '(1 2 3) '(4 5 6))
              
(1 2 3 4 5 6)





              share|improve this answer




























                4












                4








                4







                The solution of Rainer Joswig is really elegant and simple, and respects your request of using reduce.



                If you want to see also a recursive, simple solution, then here is the classical one:



                (defun concat-lists (seq1 seq2)
                
  (if (null seq1)
                
      seq2
                
      (cons (car seq1) (concat-lists (cdr seq1) seq2))))
                

                
(concat-lists '(1 2 3) '(4 5 6))
                
(1 2 3 4 5 6)





                share|improve this answer















                The solution of Rainer Joswig is really elegant and simple, and respects your request of using reduce.



                If you want to see also a recursive, simple solution, then here is the classical one:



                (defun concat-lists (seq1 seq2)
                
  (if (null seq1)
                
      seq2
                
      (cons (car seq1) (concat-lists (cdr seq1) seq2))))
                

                
(concat-lists '(1 2 3) '(4 5 6))
                
(1 2 3 4 5 6)






                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Nov 21 '18 at 15:04

























                answered Nov 21 '18 at 10:25









                RenzoRenzo

                18k43044




                18k43044























                    2














                    I do understand your requirement for 'reduce'. and here other options:



                    CL also has 'concatenante'



                    (concatenate 'list '(1 2 3) '(4 5 6))



                    There is also the other less complicated (IMHO), and not as elegant.



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (rplacd (last a) b)
                    a))



                    or



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (nconc a b)))






                    share|improve this answer





















                    • 1





                      There is no need to copy list2 in both your functions, since it will not be modified.

                      – Renzo
                      Nov 25 '18 at 10:27
















                    2














                    I do understand your requirement for 'reduce'. and here other options:



                    CL also has 'concatenante'



                    (concatenate 'list '(1 2 3) '(4 5 6))



                    There is also the other less complicated (IMHO), and not as elegant.



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (rplacd (last a) b)
                    a))



                    or



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (nconc a b)))






                    share|improve this answer





















                    • 1





                      There is no need to copy list2 in both your functions, since it will not be modified.

                      – Renzo
                      Nov 25 '18 at 10:27














                    2












                    2








                    2







                    I do understand your requirement for 'reduce'. and here other options:



                    CL also has 'concatenante'



                    (concatenate 'list '(1 2 3) '(4 5 6))



                    There is also the other less complicated (IMHO), and not as elegant.



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (rplacd (last a) b)
                    a))



                    or



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (nconc a b)))






                    share|improve this answer















                    I do understand your requirement for 'reduce'. and here other options:



                    CL also has 'concatenante'



                    (concatenate 'list '(1 2 3) '(4 5 6))



                    There is also the other less complicated (IMHO), and not as elegant.



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (rplacd (last a) b)
                    a))



                    or



                    (defun concat-lists (list1 list2)
                    (let ((a (copy-list list1))
                    (b (copy-list list2)))
                    (nconc a b)))







                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited Nov 24 '18 at 14:21

























                    answered Nov 23 '18 at 22:42









                    Ala'a MohammadAla'a Mohammad

                    8124




                    8124








                    • 1





                      There is no need to copy list2 in both your functions, since it will not be modified.

                      – Renzo
                      Nov 25 '18 at 10:27














                    • 1





                      There is no need to copy list2 in both your functions, since it will not be modified.

                      – Renzo
                      Nov 25 '18 at 10:27








                    1




                    1





                    There is no need to copy list2 in both your functions, since it will not be modified.

                    – Renzo
                    Nov 25 '18 at 10:27





                    There is no need to copy list2 in both your functions, since it will not be modified.

                    – Renzo
                    Nov 25 '18 at 10:27


















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