rust-prehistory/doc/notes/syntax.txt

we have long ago accepted the notion of a marked extended literal syntax,

  ~foo(lit,er,als) { ... a-random-string ... }

but we are going to have a symmetrical *destructuring* syntax as well, "match":

match ~foo(lit,er,als) { 
   case (case1-a-random-string) { ... normal rust code ... }
   ...
   case (caseN-a-random-string) { ... normal rust code ... }
   default { ... }
}

this permits the syntax-expander to compile a complicated
pattern-matching switch in some domain-specific syntax into an
optimized automaton. this is *extremely common* (regexps, insn decode,
AST-destructuring), almost as common as literals, and benefits real
applications tremendously since recognizer-automaton performance is
typically crucial and this lets you optimize aggressively in any case
where the patterns are static and you can lay them down in code.

example?

match ~rx {
  case ((?=<word>\w+))          { print("found a word: " + word); }
  case ([:punct:])              { npuncts++; }
}

note that the rx-matcher is completely within its rights to introduce
locals and make assignments: it just needs to embed the case arm
inside a block that performs the local bindings.