3 ms·

And this is why we have the syntax sugar.

by Twisol 8y ago

slavik81 8y ago
That introduces problems too. If you try to use sugar like '+' with an implementation that doesn't support it, you don't get any sort of error. Instead you get a different expression. Unfortunately, there's an inherent tradeoff between encoding efficiency and error detection. Notice that with the VerbalExpressions it would be trivial to return a useful error message if the 'at_least_one' pattern did not exist.
- b2gills 8y ago
  Perl 6 regexes attempt improve upon this situation by making regexes more like a regular programming language. That is it errs on the side of error detection rather than encoding efficiency. (It also adds features that would be difficult to add to Perl 5/PCRE regex design) For a start if it didn't support using `+`, then any attempt to use it would generate a compiler error because it is not alphanumeric. (regex is code in Perl 6) All non-alphanumeric characters are presumed to be metasyntactic, and so must be escaped in some way to match literally. Arguably best way is to quote it like a string literal. (Uses the same domain specific sub-language that the main language uses for string literals) / "+" + / # at least one + character It really is a significant redesign. /A{2,4}/ # Perl 5/PCRE /A ** 2..4/ # Perl 6 /A (?:BA){1,3}/x /A [BA] ** 1..3/ # Perl 6: direct translation /A ** 2..4 % B/ # Perl 6: 2 to 4 A's separated by B /A (?:BA){1,3} B?/x /A ** 2..4 %% B/ # Perl 6: %% allows trailing separator /\" [^"]* \"/x # Perl 5/PCRE /\" <-["]>* \"/ # Perl 6: direct translation /｢"｣ ~ ｢"｣ <-["]>*/ # Perl 6: between two ", match anything else # (can be used to generate better error messages) --- # Perl 5 my $foo = qr/foo/; 'abfoo' =~ /ab $foo/x; # Perl 6 my $foo = /foo/; 'abfoo' ~~ /ab <$foo>/; # or my token foo {foo} # treat it as a lexical subroutine 'abfoo' ~~ /ab <&foo>/; --- # Perl 5 my $foo = 'foo'; 'abfoo' =~ /ab \Q $foo \E/x; # treat as string not regex # Perl 6 my $foo = 'foo'; 'abfoo' ~~ /ab $foo/; # that is the default in Perl 6

And this is why we have the syntax sugar.

by Twisol 8y ago

And this is why we have the syntax sugar.

That introduces problems too. If you try to use sugar like '+' with an implementation that doesn't support it, you don't get any sort of error. Instead you get a different expression. Unfortunately, there's an inherent tradeoff between encoding efficiency and error detection. Notice that with the VerbalExpressions it would be trivial to return a useful error message if the 'at_least_one' pattern did not exist.

b2gills 8y ago
Perl 6 regexes attempt improve upon this situation by making regexes more like a regular programming language. That is it errs on the side of error detection rather than encoding efficiency. (It also adds features that would be difficult to add to Perl 5/PCRE regex design) For a start if it didn't support using `+`, then any attempt to use it would generate a compiler error because it is not alphanumeric. (regex is code in Perl 6) All non-alphanumeric characters are presumed to be metasyntactic, and so must be escaped in some way to match literally. Arguably best way is to quote it like a string literal. (Uses the same domain specific sub-language that the main language uses for string literals) / "+" + / # at least one + character It really is a significant redesign. /A{2,4}/ # Perl 5/PCRE /A ** 2..4/ # Perl 6 /A (?:BA){1,3}/x /A [BA] ** 1..3/ # Perl 6: direct translation /A ** 2..4 % B/ # Perl 6: 2 to 4 A's separated by B /A (?:BA){1,3} B?/x /A ** 2..4 %% B/ # Perl 6: %% allows trailing separator /\" [^"]* \"/x # Perl 5/PCRE /\" <-["]>* \"/ # Perl 6: direct translation /｢"｣ ~ ｢"｣ <-["]>*/ # Perl 6: between two ", match anything else # (can be used to generate better error messages) --- # Perl 5 my $foo = qr/foo/; 'abfoo' =~ /ab $foo/x; # Perl 6 my $foo = /foo/; 'abfoo' ~~ /ab <$foo>/; # or my token foo {foo} # treat it as a lexical subroutine 'abfoo' ~~ /ab <&foo>/; --- # Perl 5 my $foo = 'foo'; 'abfoo' =~ /ab \Q $foo \E/x; # treat as string not regex # Perl 6 my $foo = 'foo'; 'abfoo' ~~ /ab $foo/; # that is the default in Perl 6