String slice library
This is a library for manipulating textual content based on string slices, which are references to part of a Scheme string, and string cursors, which are pointers into strings. It is not defined whether the string slice type is disjoint from strings, or whether string cursors are a disjoint type at all. String slices are immutable, and it is an error to mutate the underlying string.
In addition, string cursors may or may not be the same as character-based indexes into strings. For example, in an implementation whose internal representation of strings is UTF-8, string cursors may be pointers to individual bytes in the string. However, the operations provided here (with the exception of those in the Compatibility section) are entirely independent of the character repertoire supported by the implementation.
This proposal contains a useful subset of SRFI 13, which manipulates strings directly with some allowances for shared substrings (which are both then and now provided only on Guile). The string operations are defined in terms of the string slice operations. Unlike SRFI 13, it does not provide start and end arguments, as their functionality is subsumed by slices. In addition, the low-level procedures are not provided, nor are any mutation operations.
Procedures marked [R7RS-small] are available in the small language, and are not exported by implementations of this proposal. They are included only for completeness.
All predicates passed to procedures defined in this proposal may be called in any order and any number of times, except as otherwise noted.
Issues
Allow negative indices in constructors?
Is string-slice-string a bad idea?
Titlecase doesn't really fit; keep it?
String constructors
In addition to the R7RS-small constructors make-string and string, the following constructors for strings are provided:
(string-tabulate proc len)
(string-unfold stop? mapper successor [ seed ])
(string-unfold-right stop? mapper successor [ seed ])
(char->string char)
String slice constructors
(string-slice-whole string)
(string-slice string start end)
(string-subslice slice start end)
(string-slice/cursors string start-cursor end-cursor)
(string-subslice/cursors string start-cursor end-cursor)
(string-slice-transform proc slice arg ...)
(char->string-slice char)
Predicates
(string-slice? obj)
(string? obj) [R7RS-small]
(string-slice-null? slice)
(string-null? string) [R7RS-small]
(string-slice-every pred slice)
(string-every pred string)
(string-slice-any pred slice)
(string-any pred string)
(string-slice-whole? slice)
(is-char? char)
(in-char-set? char-set)
Selection
string-slice-ref string-ref [R7RS-small]
string-slice-take string-take
string-slice-take-right string-take-right
string-slice-drop string-drop
string-slice-drop-right string-drop-right
string-slice-split-at string-split-at
string-slice-pad string-pad
string-slice-pad-right string-pad-right
string-slice-trim string-trim
string-slice-trim-right string-trim-right
string-slice-replicate string-replicate
Prefixes and suffixes
string-slice-prefix string-common-prefix
string-slice-suffix string-common-suffix
string-slice-prefix-length string-prefix-length
string-slice-suffix-length string-suffix-length
string-slice-prefix? string-prefix?
string-slice-suffix? string-suffix?
Searching
string-slice-index string-index
string-slice-index-right string-index-right
string-slice-skip string-skip
string-slice-skip-right string-skip-right
string-slice-count string-count
string-slice-contains string-contains
string-slice-take-while string-take-while
string-slice-drop-while string-drop-while
string-slice-break string-break
string-slice-span string-span
The whole string slice
string-slice-length string-length [R7RS-small]
string-slice-copy string-copy [R7RS-small]
string-slice-reverse string-reverse [R7RS-small]
string-slice-append string-append [R7RS-small]
string-slice-concatenate string-concatenate
string-slice-concatenate-reverse string-concatenate-reverse
string-slice-compress string-compress
Folding and mapping
string-slice-map string-map [R7RS-small]
string-slice-fold string-fold
string-slice-fold-right string-fold-right
string-slice-for-each string-for-each
string-slice-for-each-index string-for-each-index
Parsing
string-slice-tokenize string-tokenize
string-slice-split string-split
Filtering and partitioning
string-slice-filter string-filter
string-slice-remove string-remove
string-slice-partition string-partition
Functional update
string-slice-set string-set
string-slice-fill string-fill
string-slice-replace string-replace
string-slice-insert string-insert
string-slice-delete string-delete
String trees
string-tree->string write-string-tree
Compatibility
string-slice-upcase string-slice-downcase string-slice-foldcase
string-slice=? string-slice<? string-slice>?
string-slice<=? string-slice>=?
string-slice-ci=? string-slice-ci<? string-slice-ci>?
string-slice-ci<=? string-slice-ci>=?
string-slice-titlecase string-titlecase
Low-level operations
string-slice-start
string-slice-end
string-slice-string
String cursors
string-cursor-start string-cursor-end
string-cursor-ref
string-cursor-next string-cursor-previous
string-cursor-forward string-cursor-backward
string-cursor-forward-until string-cursor-backward-until
string-cursor=?
string-cursor<? string-cursor>?
string-cursor<=? string-cursor>=?
string-cursor->index string-index->cursor
string-cursors->string string-cursor-difference