Revert "Merge pull request #1192 from c410-f3r/metavar-expr"
This reverts commit 151b8196a30b1c00cb422e25f459dd4354043a6a, reversing
changes made to 0cd078da502f723f8bb1ac30ac772021e200edc9.
diff --git a/src/macros-by-example.md b/src/macros-by-example.md
index b70b94e..2c49300 100644
--- a/src/macros-by-example.md
+++ b/src/macros-by-example.md
@@ -193,53 +193,6 @@
not have the same number. This requirement applies to every layer of nested
repetitions.
-## Dollar-dollar ($$)
-
-`$$` expands to a single `$`.
-
-Since metavariable expressions always apply during the expansion of a macro, they cannot be used in recursive macro definitions and this is where `$$` expressions comes into play, i.e., `$$` can be used to resolve ambiguities in nested macros.
-
-The following example illustrates a macro that fails to compile due to the ambiguity of the repetition in a nested macro:
-
-```rust,compile_fail
-macro_rules! foo_error {
- () => {
- macro_rules! bar_error {
- ( $( $any:tt )* ) => { $( $any )* };
- // ^^^^^^^^^^^ error: attempted to repeat an expression containing no syntax variables matched as repeating at this depth
- }
- };
-}
-
-foo_error!();
-```
-
-The following resolves the problem by escaping the `$` in the repetition with `$$`:
-
-```rust
-macro_rules! foo_ok {
- () => {
- macro_rules! bar_ok {
- ( $$( $any:tt )* ) => { $$( $any )* };
- }
- };
-}
-
-foo_ok!();
-```
-
-One consequence of such expansion is that deeper nested levels make dollar-dollar declarations grown linearly, starting at `$$`, then `$$$$`, then `$$$$$` and so on. This is also necessary to be fully featured so that it is possible to specify names of metavariables using other metavariables at each nesting level.
-
-```ignore
-$foo => bar => bar // Evaluate foo at level 1
-$$foo => $foo => bar // Evaluate foo at level 2
-$$$foo => $bar => baz // Evaluate foo at level 1, and use that as a name at level 2
-$$$$foo => $$foo => $foo // Evaluate foo at level 3
-$$$$$foo => $$bar => $bar // Evaluate foo at level 1, and use that as a name at level 3
-$$$$$$foo => $$$foo => $bar // Evaluate foo at level 2, and use that as a name at level 3
-$$$$$$$foo => $$$bar => $baz // Evaluate foo at level 1, use that at level 2, and then use *that* at level 3
-```
-
## Scoping, Exporting, and Importing
For historical reasons, the scoping of macros by example does not work entirely
