How a macro is written

Decided

D-0075, settled by the language’s author: part of spec §18. Older text cites it as 18.75.

Captures read like parameters and their shapes like types: $name: kind, $xs: []K, $xs: [,]K, $x: K?, $( … )? for an optional group; built-in kinds lower-case (ident, literal, type, expr, stmt, block, code, decl), syntax rules PascalCase; macro kinds decl, stmt, expr, sharing those names. expand is shaped by #for v in $xs[,] { … }, #if $x { … } #else { … } and #error, reusing for and §12.10’s #if rather than a notation of its own. Replaces r1’s $name:#name, postfix [], (…)? groups and $xs[,] { $.f }, whose # on a kind collided with invocations and whose bare parentheses could not be told from literal ones. Matching never backtracks (§12.1–§12.3)