Metacharacter

A back-quote (`) precedes a metacharacter to cause it to be treated as an ordinary character. Since no metacharacters are alphanumeric, and since non-alphanumeric characters are always tokenized individually, back-quote only operates on the single character following it. Note that since back-quote is itself a metacharacter, two successive backquotes indicates a single back-quote should be parsed from the Avail source code.

A close-guillemet (») indicates the end of a group or other structure that started with an OPEN_GUILLEMET open-guillemet («).

The double-dagger (‡) is used within a Group to delimit the left part, which repeats, from the right part, which separates occurrences of the left part.

The double-question-mark (⁇) is a single Unicode character (U+2047). It can be placed after a token or after a simple group (a group that has no right side and does not yield anything from its left side). In the case of a token, it allows zero or one occurrences of the token to occur in the Avail source, and discards information about whether the token was encountered. Similarly, when applied to a simple group it accepts zero or one occurrences of the group's left side, discarding the distinction. In both cases, the double-question-mark causes a CompletelyOptional to be built.

An ellipsis (…) indicates that a single token should be consumed from the Avail source code (tokens are produced from the actual file content via A_Lexers). There are a few variants:

The exclamation mark (!) can follow an ELLIPSIS (…) to cause creation of a RawTokenArgument, which matches any token that isn't whitespace or a comment.

An octothorp (#) after an ELLIPSIS (…) indicates that a whole-number-valued literal token should be consumed from the Avail source code at this position. This is accomplished through the use of a RawLiteralTokenArgument.

An open-guillemet («) indicates the start of a group or other structure that will eventually end with a CLOSE_GUILLEMET (»).

A question mark (?) may follow a Simple expression, which creates an Optional, which yields a boolean literal indicating whether the token was present or not.

A section sign (§) indicates where, in the parsing of a macro invocation, it should invoke one of its prefix functions. The order of section signs in the method name corresponds with the order of the prefix functions.

A single-dagger (†) following an UNDERSCORE (_) causes creation of an ArgumentInModuleScope. This will parse an expression that does not use any variables in the local scope, then evaluate it and wrap it in a literal.

A space character separates alphanumeric tokens in a message name.

An Expression followed by a tilde (~) causes all Simple expressions anywhere within it to match case-insensitively to the tokens lexed from the Avail source code. All of these simple expressions are required to be specified in lower case to break a pointless symmetry about how to name the method.

An underscore indicates where a subexpression should be parsed.

If an up-arrow (↑) follows an UNDERSCORE, a VariableQuote is created, which expects a VariableUsePhraseDescriptor, which will be automatically converted into a reference phrase.

The vertical bar (|) separates alternatives within an Alternation. The alternatives may be Simple expressions, or simple Groups (having no double-dagger, and yielding no argument values).

The sole codepoint (Int) of this Metacharacter instance.

The Avail A_String denoting this metacharacter.