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Allow macro_rules! macros to expand to expressions or items.

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This commit is contained in:
Paul Stansifer 2012-11-07 23:13:15 -05:00 committed by Graydon Hoare
parent c946c87b6f
commit 9845a4be5a
3 changed files with 12 additions and 5 deletions
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1
src/libsyntax/ext/base.rs
View File

@ -44,6 +44,7 @@ type syntax_expander_tt_item_
enum mac_result {
mr_expr(@ast::expr),
mr_item(@ast::item),
mr_expr_or_item(fn@()-> @ast::expr, fn@()-> Option<@ast::item>),
mr_def(macro_def)
}

3
src/libsyntax/ext/expand.rs
View File

@ -81,6 +81,7 @@ fn expand_expr(exts: HashMap<~str, syntax_extension>, cx: ext_ctxt,
Some(expr_tt({expander: exp, span: exp_sp})) => {
let expanded = match exp(cx, mac.span, tts) {
mr_expr(e) => e,
mr_expr_or_item(expr_maker,_) => expr_maker(),
_ => cx.span_fatal(
pth.span, fmt!("non-expr macro in expr pos: %s",
*extname))
@ -214,6 +215,8 @@ fn expand_item_mac(exts: HashMap<~str, syntax_extension>,
mr_expr(_) => cx.span_fatal(pth.span,
~"expr macro in item position: " +
*extname),
mr_expr_or_item(_, item_maker) =>
option::chain(item_maker(), |i| {fld.fold_item(i)}),
mr_def(mdef) => {
exts.insert(mdef.name, mdef.ext);
None

13
src/libsyntax/ext/tt/macro_rules.rs
View File

@ -1,4 +1,4 @@
use base::{ext_ctxt, mac_result, mr_expr, mr_def, expr_tt};
use base::{ext_ctxt, mac_result, mr_expr_or_item, mr_def, expr_tt};
use codemap::span;
use ast::{ident, matcher_, matcher, match_tok,
match_nonterminal, match_seq, tt_delim};
@ -87,10 +87,13 @@ fn add_new_extension(cx: ext_ctxt, sp: span, name: ident,
// rhs has holes ( `$id` and `$(...)` that need filled)
let trncbr = new_tt_reader(s_d, itr, Some(named_matches),
~[rhs]);
let p = Parser(cx.parse_sess(), cx.cfg(),
trncbr as reader);
let e = p.parse_expr();
return mr_expr(e);
let p = @Parser(cx.parse_sess(), cx.cfg(),
trncbr as reader);
// Let the context choose how to interpret the result.
// Weird, but useful for X-macros.
return mr_expr_or_item(|| p.parse_expr(),
|| p.parse_item(~[/* no attrs*/]));
}
failure(sp, msg) => if sp.lo >= best_fail_spot.lo {
best_fail_spot = sp;