2.8.3.4 List and string conversion

Function: string->list str

Function: string->list str start

Function: string->list str start end

Function: list->string char-list

string->list returns a newly allocated list of the characters that make up the given string. list->string returns a newly allocated string formed from the characters in the list char-list, which must be a list of characters. string->list and list->string are inverses so far as equal? is concerned.

Function: reverse-list->string char-list

An efficient implementation of (compose list->string reverse):

(reverse-list->string '(#\a #\B #\c))
=> "cBa"

This is a common idiom in the epilog of string–processing loops that accumulate an answer in a reverse–order list. See also string-concatenate-reverse for the “chunked” variant.

Function: string-join string-list

Function: string-join string-list delimiter

Function: string-join string-list delimiter grammar

This procedure is a simple unparser: it pastes strings together using the delimiter string.

The grammar argument is a symbol that determines how the delimiter is used, and defaults to infix. Supported values for grammar are:

infix

Means an infix or separator grammar: insert the delimiter between list elements. An empty list will produce an empty string; note, however, that parsing an empty string with an infix or separator grammar is ambiguous: is it an empty list, or a list of one element, the empty string?

strict-infix

Means the same as infix, but will raise an error if given an empty list.

suffix

Means a suffix or terminator grammar: insert the delimiter after every list element. This grammar has no ambiguities.

prefix

Means a prefix grammar: insert the delimiter before every list element. This grammar has no ambiguities.

The delimiter is the string used to delimit elements; it defaults to a single space.

Examples:

(string-join '("foo" "bar" "baz") ":")
⇒ "foo:bar:baz"

(string-join '("foo" "bar" "baz") ":" 'suffix)
⇒ "foo:bar:baz:"

;; Infix grammar is ambiguous wrt empty list vs. empty string,
(string-join '()   ":") ⇒ ""
(string-join '("") ":") ⇒ ""

;; but suffix & prefix grammars are not.
(string-join '()   ":" 'suffix) ⇒ ""
(string-join '("") ":" 'suffix) ⇒ ":"