Idiomatically determine all the characters that can be used for symbols

Any Unicode character or combination of characters can be used for symbols in Raku. Here's some counting rods and some cuneiform:

sub postfix:<𒋦>($n) { say "$n trilobites" }

sub term:<𝍧> { unival('𝍧') }

𝍧𒋦

Output:

8 trilobites

And here is a Zalgo-text symbol:

sub Z̧̔ͩ͌͑̉̎A̢̲̙̮̹̮͍̎L̔ͧ́͆G̰̬͎͔̱̅ͣͫO͙̔ͣ̈́̈̽̎ͣ ($n) { say "$n COMES" }


Z̧̔ͩ͌͑̉̎A̢̲̙̮̹̮͍̎L̔ͧ́͆G̰̬͎͔̱̅ͣͫO͙̔ͣ̈́̈̽̎ͣ 'HE'

Output:

HE COMES

Of course, as in other languages, most of the characters you'll typically see in names are going to be alphanumerics from ASCII (or maybe Unicode), but that's a convention, not a limitation, due to the syntactic category notation demonstrated above, which can introduce any sequence of characters as a term or operator.

Actually, the above is a slight prevarication. The syntactic category notation does not allow you to use whitespace in the definition of a new symbol. But that leaves many more characters allowed than not allowed. Hence, it is much easier to enumerate the characters that cannot be used in symbols:

say .fmt("%4x"),"\t", uniname($_)
    if uniprop($_,'Z')
        for 0..0x1ffff;

Output:

  20    SPACE
  a0    NO-BREAK SPACE
1680    OGHAM SPACE MARK
2000    EN QUAD
2001    EM QUAD
2002    EN SPACE
2003    EM SPACE
2004    THREE-PER-EM SPACE
2005    FOUR-PER-EM SPACE
2006    SIX-PER-EM SPACE
2007    FIGURE SPACE
2008    PUNCTUATION SPACE
2009    THIN SPACE
200a    HAIR SPACE
2028    LINE SEPARATOR
2029    PARAGRAPH SEPARATOR
202f    NARROW NO-BREAK SPACE
205f    MEDIUM MATHEMATICAL SPACE
3000    IDEOGRAPHIC SPACE

We enforce the whitespace restriction to prevent insanity in the readers of programs. That being said, even the whitespace restriction is arbitrary, and can be bypassed by deriving a new grammar and switching to it. We view all other languages as dialects of Raku, even the insane ones. :-)