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ASCII Characters

MIT Scheme internally uses ASCII codes for I/O, and stores character objects in a fashion that makes it convenient to convert between ASCII codes and characters. Also, character strings are implemented as byte vectors whose elements are ASCII codes; these codes are converted to character objects when accessed. For these reasons it is sometimes desirable to be able to convert between ASCII codes and characters.

Not all characters can be represented as ASCII codes. A character that has an equivalent ASCII representation is called an ASCII character.

procedure+: char-ascii? char

Returns the ASCII code for char if char has an ASCII representation; otherwise returns #f.

In the current implementation, the characters that satisfy this predicate are those in which the Control, Super, Hyper, and Top bucky bits are turned off. All characters for which the char-bits procedure returns 0 or 1 (i.e. no bucky bits, or just Meta) count as legal ASCII characters.

procedure+: char->ascii char

Returns the ASCII code for char. An error condition-type:bad-range-argument is signalled if char doesn't have an ASCII representation.

procedure+: ascii->char code

Code must be the exact integer representation of an ASCII code. This procedure returns the character corresponding to code.

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