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( char-downcase [ char? char ] ) char?
The char-downcase procedure, given an argument that is the uppercase part of a Unicode casing pair, returns the lowercase member of the pair, provided that both characters are supported by the Scheme implementation. Note that language-sensitive casing pairs are not used. If the argument is not the uppercase member of such a pair, it is returned.
( char-foldcase [ char? char ] ) char?
The char-foldcase procedure applies the Unicode simple case-folding algorithm to its argument and returns the result. Note that language-sensitive folding is not used. If the argument is an uppercase letter, the result will be either a lowercase letter or the same as the argument if the lowercase letter does not exist or is not supported by the implementation. See UAX #29 [11] (part of the Unicode Standard) for details.
( char-upcase [ char? char ] ) char?
The char-upcase procedure, given an argument that is the lowercase part of a Unicode casing pair, returns the uppercase member of the pair, provided that both characters are supported by the Scheme implementation. Note that language-sensitive casing pairs are not used. If the argument is not the lowercase member of such a pair, it is returned.
( integer->char [ integer? n ] ) char?
Given an exact integer that is the value returned by a character when char->integer is applied to it, integer->char returns that character.
( peek-char ) ( or eof-object? char? ) ( peek-char [ input-port? port ] ) ( or eof-object? char? )
Returns the next character available from the textual input port, but without updating the port to point to the following character. If no more characters are available, an end-of-file object is returned. Note: The value returned by a call to peek-char is the same as the value that would have been returned by a call to read-char with the same port. The only diㄦence is that the very next call to read-char or peek-char on that port will return the value returned by the preceding call to peek-char. In particular, a call to peek-char on an interactive port will hang waiting for input whenever a call to read-char would have hung. (read-line) procedure
( string-ref [ string? string ] [ integer? k ] ) char?
It is an error if k is not a valid index of string. The string-ref procedure returns character k of string using zero-origin indexing. There is no requirement for this procedure to execute in constant time.