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Constructing Lists

Problem

You wish to create a list from nothingness.

Solution

Use cons, or cons-immutable to make lists or dotted pairs. cons-immutable creates an immutable dotted pair. You can also create full lists using the list function:

> (cons 1 2)
(1 . 2)
> (cons-immutable 1 '())
(1)
> (define a (list 1 2 3 4 5 6))
> a
(1 2 3 4 5 6)

If you wish to have a richer palette of tools for list creation, include SRFI 1. To create a list consisting of n copies of the same fill value, use make-list. You can also create a list consisting of several values, with the last forming the tail of the constructed list, using the cons* function.

%begin scheme% > (require (lib "list.ss" "srfi" "1"))
> (define c (cons* 1 2 3 4 5))
> c
(1 2 3 4 . 5) > (define d (make-list 15 #\c))
> d
(#\c #\c #\c #\c #\c #\c #\c #\c #\c #\c #\c #\c #\c #\c #\c) %end%

Discussion

buildlist, cons* etc.

Comments about this recipe

Contributors

-- NoelWelsh - 02 Jun 2004