- (string-filter char/char-set/pred s [start end]) -> stringprocedure
- (string-delete char/char-set/pred s [start end]) -> stringprocedure
Filter the string S, retaining only those characters that satisfy / do not satisfy the CHAR/CHAR-SET/PRED argument. If this argument is a procedure, it is applied to the character as a predicate; if it is a char-set, the character is tested for membership; if it is a character, it is used in an equality test.
If the string is unaltered by the filtering operation, these functions may return either S or a copy of S.