mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Minor doc updates.

Browse Source
This commit is contained in:
Paul Stansifer 2012-08-24 17:49:03 -07:00
parent 7669032dd3
commit 9297d1f00a
2 changed files with 19 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
doc/rust.md
View File

@ -522,7 +522,8 @@ matches, in a structure that mimics the structure of the repetition
encountered on a successful match. The job of the transcriber is to sort that
structure out.
The rules for transcription of these repetitions are called "Macro By Example". Essentially, one "layer" of repetition is discharged at a time, and all of
The rules for transcription of these repetitions are called "Macro By Example".
Essentially, one "layer" of repetition is discharged at a time, and all of
them must be discharged by the time a name is transcribed. Therefore,
`( $( $i:ident ),* ) => ( $i )` is an invalid macro, but
`( $( $i:ident ),* ) => ( $( $i:ident ),* )` is acceptable (if trivial).
@ -537,6 +538,20 @@ transcribes to `( (a,d), (b,e), (c,f) )`.
Nested repetitions are allowed.
### Parsing limitations
The parser used by the macro system is reasonably powerful, but the parsing of
Rust syntax is restricted in two ways:
1. The parser will always parse as much as possible. If it attempts to match
`$i:expr [ , ]` against `8 [ , ]`, it will attempt to parse `i` as an array
index operation and fail. Adding a separator can solve this problem.
2. The parser must have eliminated all ambiguity by the time it reaches a
`$` _name_ `:` _designator_. This most often affects them when they occur in
the beginning of, or immediately after, a `$(...)*`; requiring a distinctive
token in front can solve the problem.
## Syntax extensions useful for the macro author
* `log_syntax!` : print out the arguments at compile time

5
doc/tutorial.md
View File

@ -2481,8 +2481,9 @@ Macros, as currently implemented, are not for the faint of heart. Even
ordinary syntax errors can be more difficult to debug when they occur inside
a macro, and errors caused by parse problems in generated code can be very
tricky. Invoking the `log_syntax!` macro can help elucidate intermediate
states, and using `--pretty expanded` as an argument to the compiler will
show the result of expansion.
states, using `trace_macros!(true)` will automatically print those
intermediate states out, and using `--pretty expanded` as an argument to the
compiler will show the result of expansion.
# Traits