— Scheme Procedure: string-map proc s [start [end]]

Return a new string made by mapping procedure proc over s. proc is a character-to-character procedure. The order in which the procedure is applied to the string elements is not specified.

— Scheme Procedure: string-map! proc s [start [end]]

Map procedure proc over s, modifying it in-place. proc is a character-to-character procedure. The order in which the procedure is applied to the string elements is not specified.

— Scheme Procedure: string-fold kons knil s [start [end]]

Fold kons over the characters of s, with knil as the terminating element, from left to right. kons is called with two arguments: The actual character and the last result of kons' application.

— Scheme Procedure: string-unfold p f g seed [base [make-final]]

Return a new string constructed as specified by procedures p, f, and g, given an initial value seed. More precisely:

• g is used to generate a series of seed values from the initial seed: seed, (g seed), (g^2 seed), (g^3 seed), ...
• p tells us when to stop — when it returns true when applied to one of these seed values.
• f maps each seed value to the corresponding character in the result string. These chars are assembled into the string in a left-to-right order.
• base is the optional initial/leftmost portion of the constructed string. It defaults to the empty string.
• make-final is applied to the terminal seed value (on which p returns true) to produce the final/rightmost portion of the constructed string. It defaults to (lambda (x) "").

— Scheme Procedure: string-for-each proc s [start [end]]

Map proc over the characters in s in ascending order.