How can I reverse a list?

by

Use:

(define (reverse1 l)
  (if (null? l)
     nil
     (append (reverse1 (cdr l)) (list (car l)))
  )
)

Explanation:

Rules:

  1. If the list is empty, then the reverse list is also empty
  2. Else behind the reverse tail of the list, add the first element of the list

Look at this code this way:

reverse1 is name of the function and l is a parameter. If the list is empty then the reverse is also empty.
Else call the reverse1 function with (cdr l) which is the tail of the list and append that to the first alement (car l) that you make as a list.

In your example (pseudocode):

1st iteration
l=>(a (bcd)e)
car l => a
cdr l => (bcd)e
list(car l) =>(a)
------------------
reverse( cdr l)"+"(a)
------------------
2nd iteration
l=>((bcd)e)
car l => (bcd)
cdr l =>e
list(car l)=>(bcd)
--------------------
reverse(cdr l)"+"((bcd))+(a)
-----------------------
3rd iteration
l=>e
car l=> e
cdr l => nil
list (car l) =>(e)
-------------------------
(e (bcd)a)

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