Exercise 1.2.5

More Characters

While not portable, and not part of the Common Lisp standard, in SBCL and a few other Lisp implementations, you can refer to any character beyond the ASCII-range using a character object with its Unicode name, simply replacing the space word-separators with underscores (_). This is a little unusual for the Lisp world, since symbol names normally use the - (hyphen/dash) character as the word-separator; but as I said in Section 1.1.3, the Common Lisp Style Guide, that is a naming convention, which in this case isn't followed.

Some of these characters you've seen before, but lets go through a few so you get used to typing them out:

#\subscript_three
#\greek_small_letter_lamda
#\greek_capital_letter_sigma
#\cuneiform_sign_an_plus_naga_opposing_an_plus_naga

These names are not case-sensitive: you could type #\Greek_Small_Letter_Lamda, #\GREEK_SMALL_LETTER_LAMDA, or even #\gReEK_sMaLl_LeTtER_lAmDA, and the Lisp reader will see it the same---for style and legibility of your code, however, you should stick with the lower-case names. You can use this syntax to enter any Unicode character into the SBCL REPL.

What You Should See

* #\subscript_three
#\SUBSCRIPT_THREE
* #\greek_small_letter_lamda
#\GREEK_SMALL_LETTER_LAMDA
* #\greek_capital_letter_sigma
#\GREEK_CAPITAL_LETTER_SIGMA
* #\cuneiform_sign_an_plus_naga_opposing_an_plus_naga
#\CUNEIFORM_SIGN_AN_PLUS_NAGA_OPPOSING_AN_PLUS_NAGA

When you enter a character object at the REPL, it returns itself. When you want the character's glyph, i.e., what it will look like in a string, you need to put the character into a string. This will be covered in a later exercise.