🎯 Token Category Operators: The @ and ! Prefixes

[not implemented yet]

The @ and ! operators are powerful prefixes used inside pattern variable syntax ({...}) to match tokens based on their lexical category rather than their literal text. This is the core mechanism that makes uCalc's Transformer token-aware, giving it a structural understanding of text that traditional regular expressions lack.

The @ Operator: Matching by Category

The @ operator is the standard way to match a token based on its type. Instead of looking for a specific word like "if", you can look for any alphanumeric identifier using {@Alphanumeric}.

Syntax

• {@Category}: Matches any token belonging to Category but does not capture its value.
• {@Category:varName}: Matches any token belonging to Category and captures its text into the variable {varName}.

This makes patterns both readable and robust. A pattern to find a number is simply {@Number}, which is far clearer than a complex regex like [-+]?[0-9]*\.?[0-9]+.

For a complete list of categories, see the Matching by token category topic.

The ! Operator: Negating a Category

The ! operator is the logical inverse of @. It matches any token that does not belong to the specified category. This is extremely useful for capturing 'everything else' or for defining boundaries in a pattern.

Syntax

• {!Category}: Matches any token that is not in Category.
• {!Category:varName}: Matches and captures any token that is not in Category.

For example, the pattern {!Bracket:content} will capture any token as long as it isn't an opening or closing bracket. This is a simple and powerful way to capture the content between delimiters.

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