2.8.3.2 Predicates

Function: string? obj

Return #t if obj is a string, otherwise return #f.

Function: string-null? str

Return #t if str is the empty string, otherwise return #f.

Function: string-every char/char-set/pred str

Function: string-every char/char-set/pred str start

Function: string-every char/char-set/pred str start end

Check to see if the given criteria is true of every character in str, proceeding from left (index start) to right (index end).

If char/char-set/pred is a character, it is tested for equality with the elements of str.

If char/char-set/pred is a character set, the elements of str are tested for membership in the set.

If char/char-set/pred is a predicate procedure, it is applied to the elements of str. The predicate is “witness–generating”: if string-every returns true, the returned true value is the one produced by the final application of the predicate to str[end]. If string-every is applied to an empty sequence of characters, it simply returns #t.

If string-every applies the predicate to the final element of the selected sequence (i.e. s[end-1]), that final application is a tail call.

The names of this procedure does not end with a question mark; this is to indicate that, in the predicate case, they do not return a simple boolean (#t or #f), but a general value.

Function: string-any char/char-set/pred str

Function: string-any char/char-set/pred str start

Function: string-any char/char-set/pred str start end

Check to see if the given criteria is true of every/any character in str, proceeding from left (index start) to right (index end).

If char/char-set/pred is a character, it is tested for equality with the elements of str.

If char/char-set/pred is a character set, the elements of str are tested for membership in the set.

If char/char-set/pred is a predicate procedure, it is applied to the elements of str. The predicate is “witness–generating”: if string-any returns true, the returned true value is the one produced by the application of the predicate.

If string-any applies the predicate to the final element of the selected sequence (i.e. s[end-1]), that final application is a tail call.

The name of this procedures does not end with a question mark; this is to indicate that, in the predicate case, they do not return a simple boolean (#t or #f), but a general value.