Sum of numbers in a list

[Jonathan Handojo]

Hello fellow hackers,

 

This post probably doesn't reflect the title as what you think it is, but I think it will still do. What I want to achieve is from a list of integers or reals as example below:

 

(1 2 3 4 5 6 7)

 

into:

 

(1 3 6 10 15 21 28)

 

where the value on the nth index is the sum of all the integers from the first index to that index. Anyone know a good way to achieve this?

I'm hoping to use a simple mapcar function but nothing's coming to my head. 

 

(P.S. I've run an error handle so that only integers and reals are allowed in the list.)

 

Thanks,

Jonathan Handojo

[Lee Mac]

(defun foo ( l )
    (defun bar ( l )
        (if l (cons (apply '+ l) (bar (cdr l))))
    )
    (reverse (bar (reverse l)))
)

_$ (foo '(1 2 3 4 5 6 7))
(1 3 6 10 15 21 28)

 

Edited November 30, 2019 by Lee Mac

[Lee Mac]

(defun foo ( l / x )
    (setq x 0)
    (mapcar '(lambda ( y ) (setq x (+ x y))) l)
)

_$ (foo '(1 2 3 4 5 6 7))
(1 3 6 10 15 21 28)

 

Edited November 30, 2019 by Lee Mac

[Jonathan Handojo]

2 minutes ago, Lee Mac said:

(defun foo ( l / x )
    (setq x 0)
    (mapcar '(lambda ( y ) (setq x (+ x y))) l)
)

_$ (foo '(1 2 3 4 5 6 7))
(1 3 6 10 15 21 28)

 

 

That was quick! What a nice method, I thought I would've used apply on some case, but that's a nice trick. Thanks Lee!

[Grrr]

Not elegant as Lee's : 

; (foo '(1 2 3 4 5 6 7))
(defun foo ( L )
  ('( (f) (cdr (f 0 L)))
    '( (c L)
      (if L
        (cons c (f (+ c (car L)) (cdr L)))
        (list c)
      )
    )
  )
)