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 indexes of 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 also 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 of this proposal 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 with the same names and functions as SRFI-13 procedures are marked [SRFI 13]; note that they don't necessarily support all of the arguments of the SRFI 13 versions.
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.
(make-string k [ char ]) [R7RS-small]
Returns a string containing k characters, all of which are char. If char is omitted, the contents of the string are implementation-dependent.
(string char ...) [R7RS-small]
(string-unfold stop? mapper successor [ seed ])
(string-unfold-right stop? mapper successor [ seed ])
(string-slice->string string-slice)
Returns a string which contains the characters of string-slice in order.
(make-string-slice string start end)
Returns a string-slice which contains the characters of string in order from start (inclusive) to end (exclusive).
(string-slice char ...)
(string-slice-subslice slice start end)
(string->string-slice string)
Returns a string slice which contains the characters of string in order.
(string-slice/cursors string start-cursor end-cursor)
(string-subslice/cursors string start-cursor end-cursor)
(string-slice-transform proc slice obj ...)
Proc is a procedure which accepts a string as its first argument and returns a string. It is invoked on a string which contains the characters of slice in order plus the obj arguments, if any. The resulting string is returned as a string slice by string-slice-transform. This procedure allows string-based procedures to be easily used in an environment that provides and expects string slices.
(string-slice? obj)
(string? obj) [R7RS-small]
Returns #t if obj is a string slice, and #f otherwise.
(string-slice-null? slice)
(string-null? string) [SRFI 13]
Returns #t if slice contains zero characters, and #f otherwise.
(string-slice-every pred slice)
(string-every pred string) [SRFI 13]
Returns #t if pred returns true for every character in slice'', and #f otherwise.
(string-slice-any pred slice)
(string-any pred string) [SRFI 13]
Returns #t if pred returns true for any character in slice'', and #f otherwise.
(is-char? char)
Returns a predicate which accepts one argument, and returns #t if the argument is the same as char (in the sense of char=?) and #f otherwise.
(in-char-set? char-set)
Returns a predicate which accepts one argument, and returns #t if the argument is an element of char-set, a SRFI 14 character set, and #f otherwise.
(string-slice-ref slice k)
(string-ref string k) [R7RS-small]
Returns the 'k'th character of slice, starting with 0. It is an error if k is not a non-negative exact integer less than the length of slice.
(string-slice-take slice n)
(string-take string n) [SRFI 13]
Returns a string slice which contains the first n characters of slice.
(string-slice-take-right slice n)
(string-take-right string n) [SRFI 13]
Returns a string slice which contains the last n characters of slice.
(string-slice-drop slice n)
(string-drop string n) [SRFI 13]
Returns a string slice which contains all but the first n characters of slice.
(string-slice-drop-right slice n)
(string-drop-right string n) [SRFI 13]
Returns a string slice which contains all but the last n characters of slice.
(string-slice-split-at slice n)
(string-split-at string n) [SRFI 13]
Returns two values, a string slice containing the first n characters of slice, and another string slice containing the remaining characters of slice.
(string-slice-replicate slice from to)
(string-replicate string from to)
(string-slice-pad slice len [ char ])
(string-pad string len [ char ]) [SRFI 13]
(string-slice-trim slice len [ char ])
(string-trim string len [ char ]) [SRFI 13]
(string-slice-trim-right slice len [ char ])
(string-trim-right string len [ char ]) [SRFI 13]
(string-slice-trim-both slice len [ char ])
(string-trim-both string len [ char ]) [SRFI 13]
(string-slice-compress slice [ char ])
(string-compress string [ char ])
(string-slice-prefix slice1 slice2)
(string-prefix string1 string2)
(string-slice-suffix slice1 slice2)
(string-suffix string1 string2) [SRFI 13]
(string-slice-prefix-length slice1 slice2)
(string-prefix-length string1 string2)
(string-slice-suffix-length slice1 slice2) [SRFI 13]
(string-suffix-length string1 string2)
(string-slice-prefix? slice1 slice2)
(string-prefix? string1 string2) [SRFI 13]
(string-slice-suffix? slice1 slice2)
(string-suffix? string1 string2) [SRFI 13]
(string-slice-count proc slice)
(string-count proc string) [SRFI 13]
(string-slice-take-while proc slice)
(string-take-while proc string) [SRFI 13]
(string-slice-drop-while proc slice)
(string-drop-while proc string) [SRFI 13]
(string-slice-break proc slice)
(string-break proc string) [SRFI 13]
(string-slice-drop proc slice)
(string-drop proc string) [SRFI 13]
(string-slice-contains slice1 slice2)
(string-contains string1 string2) [SRFI 13]
(string-slice-length slice)
(string-length string) [R7RS-small]
(string-slice-copy slice)
(string-copy string [ start [ end ] ]) [R7RS-small]
(string-slice-reverse slice)
(string-reverse slice) [SRFI 13]
(string-slice-append slice ...)
(string-append string ...) [R7RS-small]
(string-slice-concatenate list-of-slices)
(string-concatenate list-of-strings) [SRFI 13]
(string-slice-concatenate-reverse list-of-slices)
(string-concatenate-reverse list-of-strings) [SRFI 13]
(string-slice-map proc slice ...)
(string-map proc string ...) [R7RS-small]
(string-slice-for-each proc slice ...)
(string-for-each proc string ...) [R7RS-small]
(string-slice-fold proc nil slice)
(string-fold proc nil string) [R7RS-small]
(string-slice-fold-right proc nil slice)
(string-fold-right proc nil string) [R7RS-small]
(string-slice-split slice [sep [ limit'' ] ])
(string-slice-split slice [sep [ limit'' ] ])
Returns a list of the words contained in slice. If sep (which is also a string slice) is omitted, then the words are separated by arbitrary strings of whitespace characters (those on which char-whitespace? returns #t). If sep is supplied, it specifies a string to be used as the word separator. The returned list will then have one more item than the number of non-overlapping occurrences of the separator in the string. If sep is empty, then the returned list contains a list of the characters in slice.
If limit is provided, at most that many splits occur, and the remainder of slice is returned as the final element of the list (thus, the result will have at most limit + 1 elements). If limit is not specified, then all possible splits are made. It is an error if limit is not a positive exact integer.
(string-slice-filter proc slice) [SRFI 13]
(string-filter proc string)
(string-slice-remove proc slice)
(string-remove proc string)
(string-slice-partition proc slice)
(string-partition proc string)
(string-slice->list slice)
(string-slice->vector slice)
(string->list string [ start [ end ] ]) [R7RS-small]
(list->string list[ start [ end ] ]) [R7RS-small]
(string->vector string[ start [ end ] ]) [R7RS-small]
(vector->string vector[ start [ end ] ]) [R7RS-small]