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REGEXP.md

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Regular Expressions in Quamina

Regular Expressions (hereinafter “regexps”) may appear in Quamina Regexp Patterns.

Syntax

The regexp syntax supported in Regexp Patterns are that specified in RFC 9485, I-Regexp: An Interoperable Regular Expression Format.

There is one important syntactic difference. The backslash character “\” commonly used in regexp constructs for escaping metacharacters (as in Stop\.) and in such constructs such as \P{Lu}, is “~” in Quamina regexps.

“” is used for this purpose because “\” is also used in Go string literals and in JSON. Thus, complexity is added to unit testing and fragments such as \\\\ and even \\\\\\\\ are regularly needed. Conventional regexps may be turned into Quamina regexps by replacing occurrences of “\” with “” wherever “\” is being used as a metacharacter. If a Quamina regexp needs to match the literal character “\”, it need not be escaped. For example, the common Go-language syntax for representing whitespace characters in code can be matched with the Quamina regexp \[nrt], but the newline character, U+000A, would be matched by the Quamina regexp ~n.

When a regexp is used in a Quamina addPattern() call, an error is returned if the regexp contains a syntax error or if it uses a regexp feature that is not yet supported in the current release.

Features

Regexps are being added to Quamina incrementally. The following list identifies the full set of planned features; it is not in any particular order. Those that are supported in the current release are bold-faced.

. : single-character matcher

| : logical alternatives

[] : character-class matcher

() : parenthetized sub-regexp

* : zero-or-more matcher

+ : one-or-more matcher

? : optional matcher

{lo,hi} : occurrence-count matcher

~p{} : Unicode property matcher

~P{} : Unicode property-complement matcher

[^] : complementary character-class matcher

Semantics of “.”

In Quamina regexps, the . metacharacter matches any Unicode character whose code point is among the Unicode Scalars as defined in Definition D76 in Section 3.9 of the Unicode Standard. This is the range of codepoints between U+0000 - U+D7FF inclusive, and U+E000 - U+10FFFF inclusive.

Put another way, . matches all of the Unicode code points except those defined in the Unicode Standard as “Surrogates”.