Unicode constant

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

perl -Mutf8 -MMath::Trig -E 'use constant π => pi; say π'

3.14159265358979

perl -Mutf8 -MMath::Trig=:pi -C -E 'use constant π² => pi2; say π²'

Unrecognized character \x{b2}; marked by <-- HERE after constant π<-- HERE near column 15 at -e line 1.

perl -Mutf8 -MMath::Trig=:pi -C -E 'use constant q(π²) => pi2; say π²'

Constant name 'π²' has invalid characters at -e line 1. BEGIN failed--compilation aborted at -e line 1.

Comment on Unicode constant

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Re: Unicode constant by haukex (Archbishop) on Nov 07, 2019 at 07:39 UTC
From Identifier parsing: If working under the effect of the `use utf8;` pragma, the following rules apply: `/ (?[ ( \p{Word} & \p{XID_Start} ) + [_] ]) (?[ ( \p{Word} & \p{XID_Continue} ) ]) * /x` [download] And looking at the Unicode Character Properties of U+00B2 SUPERSCRIPT TWO, it's neither `XID_Start` nor `XID_Continue`. Although I'm not an expert on Unicode identifiers, this seems like it explains it.	[reply] [d/l] [select]
Re^2: Unicode constant by ikegami (Patriarch) on Nov 07, 2019 at 09:40 UTC
Basically, identifiers can't contain symbols except "`_`". They can't contain "`²`" any more than "`!`". (Punctuation variables excepted.)	[reply] [d/l] [select]
Re: Unicode constant by Anonymous Monk on Nov 08, 2019 at 00:49 UTC
Yes, the Perl parser's rules for identifiers considerably predates the entire concept of UTF8 ... and, for whatever it is worth, even today most programming languages are the same.	[reply]
Re^2: Unicode constant by Anonymous Monk on Nov 08, 2019 at 01:33 UTC
Still pretty impressive, Perl is, TIMTOWTDI: perl -Mutf8 -MMath::Trig=:pi -C -E 'use constant π2 => pi2; say π2' 6.28318530717959	[reply]