2.40.6.4 Selectors

Function: value icar ipair

Function: value icdr ipair

These procedures return the contents of the icar and icdr field of their argument, respectively. Note that it is an error to apply them to the empty ilist.

(icar (iq a b c))       ⇒  a
(icdr (iq a b c))       ⇒  (b c)

(icar (iq (a) b c d))   ⇒  (a)
(icdr (iq (a) b c d))   ⇒  (b c d)

(icar (ipair 1 2))      ⇒  1
(icdr (ipair 1 2))      ⇒  2

(icar '())              error→  invalid argument
(icdr '())              error→  invalid argument

Function: value icaar ipair

Function: value icadr ipair

Function: value icdar ipair

Function: value icddr ipair

Compositions of icar and icdr.

Function: value icaaar ipair

Function: value icaadr ipair

Function: value icadar ipair

Function: value icaddr ipair

Function: value icdaar ipair

Function: value icdadr ipair

Function: value icddar ipair

Function: value icdddr ipair

Compositions of icar and icdr.

Function: value icaaaar ipair

Function: value icaaadr ipair

Function: value icaadar ipair

Function: value icaaddr ipair

Function: value icadaar ipair

Function: value icadadr ipair

Function: value icaddar ipair

Function: value icadddr ipair

Function: value icdaaar ipair

Function: value icdaadr ipair

Function: value icdadar ipair

Function: value icdaddr ipair

Function: value icddaar ipair

Function: value icddadr ipair

Function: value icdddar ipair

Function: value icddddr ipair

Compositions of icar and icdr.

Function: value ilist-ref ilist i

Return the i-th element of ilist. (This is the same as the icar of (idrop ilist i).) It is an error if ‘i >= n’, where n is the length of ilist.

(ilist-ref (iq a b c d) 2)      ⇒ c

Function: object ifirst ipair

Function: object isecond ipair

Function: object ithird ipair

Function: object ifourth ipair

Function: object ififth ipair

Function: object isixth ipair

Function: object iseventh ipair

Function: object ieighth ipair

Function: object ininth ipair

Function: object itenth ipair

Synonyms for icar, icadr, icaddr, …

(ithird '(a b c d e))           ⇒ c

Function: x y icar+icdr ipair

The fundamental ipair deconstructor:

(lambda (p) (values (icar p) (icdr p)))

This can, of course, be implemented more efficiently by a compiler.

Function: ilist itake x i

Function: object idrop x i

Function: object ilist-tail x i

itake returns the first i elements of ilist x. idrop returns all but the first i elements of ilist x. ilist-tail is either the same procedure as idrop or else a procedure with the same behavior.

(itake (iq a b c d e)  2)       ⇒ (a b)
(idrop (iq a b c d e)  2)       ⇒ (c d e)

x may be any value: a proper or dotted ilist:

(itake (ipair 1 (ipair 2 (ipair 3 'd)))         ⇒ (1 2)
(idrop (ipair 1 (ipair 2 (ipair 3 'd))) 2)      ⇒ (3 . d)
(itake (ipair 1 (ipair 2 (ipair 3 'd))) 3)      ⇒ (1 2 3)
(idrop (ipair 1 (ipair 2 (ipair 3 'd))) 3)      ⇒ d

For a legal i, itake and idrop partition the ilist in a manner which can be inverted with iappend:

(iappend (itake x i) (idrop x i))       ⇒ x

idrop is exactly equivalent to performing i icdr operations on x; the returned value shares a common tail with x.

Function: ilist itake-left x i

Function: object idrop-left x i

Aliases for itake and idrop.

NOTE These syntactic bindings are Vicare extensions.

Function: object itake-right dilist i

Function: object idrop-right dilist i

Return the last i elements of dilist. idrop-right returns all but the last i elements of dilist.

(itake-right (iq a b c d e) 2)  ⇒ (d e)
(idrop-right (iq a b c d e) 2)  ⇒ (a b c)

The returned ilist may share a common tail with the argument ilist.

dilist may be any ilist, either proper or dotted:

(itake-right (iq ipair 1 (ipair 2 (ipair 3 'd))) 2)     ⇒ (2 3 . d)
(idrop-right (ipair 1 (ipair 2 (ipair 3 'd))) 2)        ⇒ (1)
(itake-right (ipair 1 (ipair 2 (ipair 3 'd))) 0)        ⇒ d
(idrop-right (ipair 1 (ipair 2 (ipair 3 'd))) 0)        ⇒ (1 2 3)

For a legal i, itake-right and idrop-right partition the ilist in a manner which can be inverted with iappend:

(iappend (itake dilist i) (idrop dilist i)) ⇒ dilist

itake-right’s return value is guaranteed to share a common tail with dilist.

Function: ilist object isplit-at x i

Split the ilist x at index i, returning an ilist of the first i elements, and the remaining tail. It is equivalent to:

(values (itake x i) (idrop x i))

Function: object ilast ipair

Function: ipair last-ipair ipair

Return the last element of the non–empty, possibly dotted, ilist ipair. last-ipair returns the last ipair in the non–empty ilist pair.

(ilast (iq a b c))              ⇒ c
(last-ipair (iq a b c))         ⇒ (c)