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11.26 srfi-130 - Cursor-based string library

Module: srfi-130

This is an reduced version of srfi-13 that supports cursors in addition to indexes. The consistency with R7RS and recent srfis are also considered.

Gauche supports string cursors natively (see String cursors), so all built-in and srfi-13 string procedures that takes string indexes can als otake string cursors as well. You want to use this module explicitly, though, if you’re writing a portable code.

The following are built-in. See String cursors, for the details.

string-cursor?        string-cursor-start    string-cursor-end
string-cursor-next    strig-cursor-prev      string-cursor-forward
string-cursor-back    string-cursor=?        string-cursor<?
string-cursor<=?      string-cursor>?        string-cursor>=?
string-cursor-diff    string-cursor->index   string-index->cursor

The following procedures are simply aliases of the builtin version without the /cursor or /cursors suffix.

string->list/cursors  string->vector/cursors string-copy/cursors
string-ref/cursor     substring/cursors

The following procedures are defined in srfi-13. See String library, for the details. Note: Some of those procedures in srfi-13 accept only indexes. In srfi-130, both indexes and cursors are accepted. Our srfi-13 implementation shares the same procedure with srfi-130, so they accept both indexes and cursors but such code won’t be portable as srfi-13.

string-null?       string-any         string-every       string-tabulate
string-unfold      string-unfold-right                   reverse-list->string
string-take        string-drop        string-take-right  string-drop-right
string-pad         string-pad-right   string-trim        string-trim-right
string-trim-both   string-replace     string-prefix-length
string-suffix-length                  string-prefix?     string-suffix
string-concatenate string-concatenate-reverse            string-count
string-filter      string-reverse

The following procedures are the same as srfi-152, except that the arguments that takes integer indexes can also accept string cursors (see String library (reduced)):

string-replicate   string-remove      string-split

The following procedures are also defined in srfi-13, but srfi-130 redefines them to return a string cursor instead of an integer index. They are described below.

string-index        string-index-right
string-skip         string-skip-right
string-contains     string-contains-right
Function: string-index string pred :optional start end
Function: string-index-right string pred :optional start end
Function: string-skip string pred :optional start end
Function: string-skip-right string pred :optional start end

[SRFI-130] {srfi-130} Find the position of a character that satisfies pred (string-index/string-index-right), or does not satisfy pred (string-skip/string-skip-right), in a string.

While srfi-13’s procedures of the same names returns integer index, these returns a string cursor instead.

They always return a string cursor. The returned cursor from string-index/string-skip points the leftmost character that satisfies/does not satsify pred, while the returned cursor from string-index-right points the next (right) character of the rightmost one that satisfies/does not satisfy pred. If there’s no character that satisfies/does not satisfy pred, string-index and string-skip returns a cursor at the end of the string, while string-index-right and string-skip-right returns a cursor at the beginning of the string.

(This is easier to understand if you think the cursor is between characters; if we scan a string from left to right, the cursor looks at the character on its right; if we scan from right to left, the cursor looks at the character on its left.)

The optional start/end can be string cursors or integer indexes to limit the region of string to search.

(define *s* "abc def ghi")

(string-cursor->index *s* (string-index *s* char-whitespace?))
  ⇒ 3

(string-cursor->index *s* (string-index *s* char-whitespace? 4))
  ⇒ 7

(string-cursor->index *s* (string-index-right *s* char-whitespace?))
  ⇒ 8

(string-cursor->index *s* (string-index-right *s* char-whitespace? 0 7))
  ⇒ 4
Function: string-contains haystack needle :optional start1 end1 start2 end2
Function: string-contains-right haystack needle :optional start1 end1 start2 end2

[SRFI-130] {srfi-130} Search for a substring needle in a string haystack. The substring is searched from left to right (string-contains) or right to left (string-contains-right).

While srfi-13’s procedures of the same names returns an integer index when a substring is found, these procedures returns a string curosr of haystack.

If haystack doesn’t countain needle, they return #f.

Function: string-for-each-cursor proc string :optional start end

[SRFI-130] {srfi-130} Calls proc with each cursor of string, from left to right, excluding the post-end cursor. This is the cursor version of string-for-each-index in srfi-13 (see SRFI-13 String mapping).


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