Exercise 1.2.6
Character Codes
Character objects all have numeric values, called codes, corresponding to either the code-points in the Unicode table, or the current encoding of your running Lisp image. Lisp comes with a lot of useful tools for working with characters and strings as numbers and vectors/arrays, and where the standard falls short, there are several popular libraries you can always rely on.
You can get the code for a character object with the function char-code, and the character object for a code with code-char, as follows:
(code-char #x61)
(char-code #\a)
See the symbol #x61 in the example above? That's the hexadecimal (base-16) number 0x61, which is 97 in decimal (base-10). Sometimes it's more convenient to reference integers using a different notation than decimal. The Unicode tables are listed using hexadecimal, for instance---so you can just type the hex-number using the Sharpsign-X syntax. There will be more discussion on numbers and notation in Chapter 1.6.
What You Should See
* (code-char #x61)
#\a
* (char-code #\a)
97
Learn Lisp The Hard Way by "the Phoeron" Colin J.E. Lupton is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.