Node:Append/Reverse, Next:List Modification, Previous:List Selection, Up:Lists
append and append! are used to concatenate two or more
lists in order to form a new list. reverse and reverse!
return lists with the same elements as their arguments, but in reverse
order. The procedure variants with an ! directly modify the
pairs which form the list, whereas the other procedures create new
pairs. This is why you should be careful when using the side-effecting
variants.
| append . args | Scheme Procedure |
| scm_append (args) | C Function |
Return a list consisting of the elements the lists passed as
arguments.
(append '(x) '(y)) => (x y) (append '(a) '(b c d)) => (a b c d) (append '(a (b)) '((c))) => (a (b) (c))The resulting list is always newly allocated, except that it shares structure with the last list argument. The last argument may actually be any object; an improper list results if the last argument is not a proper list. (append '(a b) '(c . d)) => (a b c . d) (append '() 'a) => a |
| append! . lists | Scheme Procedure |
| scm_append_x (lists) | C Function |
A destructive version of append (see Pairs and lists). The cdr field
of each list's final pair is changed to point to the head of
the next list, so no consing is performed. Return a pointer to
the mutated list.
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| reverse lst | Scheme Procedure |
| scm_reverse (lst) | C Function |
| Return a new list that contains the elements of lst but in reverse order. |
| reverse! lst [new_tail] | Scheme Procedure |
| scm_reverse_x (lst, new_tail) | C Function |
A destructive version of reverse (see Pairs and lists). The cdr of each cell in lst is
modified to point to the previous list element. Return a pointer to the
head of the reversed list.
Caveat: because the list is modified in place, the tail of the original
list now becomes its head, and the head of the original list now becomes
the tail. Therefore, the lst symbol to which the head of the
original list was bound now points to the tail. To ensure that the head
of the modified list is not lost, it is wise to save the return value of
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