implement `env!`

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 6c93dbc..c2b9e33 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -30,11 +30,14 @@ enum syntax_extension {
 fn syntax_expander_table() -> hashmap<str, syntax_extension> {
     fn builtin(f: syntax_expander_) -> syntax_extension
         {normal({expander: f, span: none})}
+    fn builtin_tt(f: syntax_expander_tt_) -> syntax_extension
+        {normal_tt({expander: f, span: none})}
     let syntax_expanders = str_hash::<syntax_extension>();
     syntax_expanders.insert("fmt", builtin(ext::fmt::expand_syntax_ext));
     syntax_expanders.insert("auto_serialize",
                             item_decorator(ext::auto_serialize::expand));
     syntax_expanders.insert("env", builtin(ext::env::expand_syntax_ext));
+    syntax_expanders.insert("env2", builtin_tt(ext::env2::expand_syntax_ext));
     syntax_expanders.insert("macro",
                             macro_defining(ext::simplext::add_new_extension));
     syntax_expanders.insert("concat_idents",
diff --git a/src/libsyntax/ext/env2.rs b/src/libsyntax/ext/env2.rs
new file mode 100644
index 0000000..0a5da2e
--- /dev/null
+++ b/src/libsyntax/ext/env2.rs
@@ -0,0 +1,46 @@
+import base::*;
+export expand_syntax_ext;
+import ast::{matcher, matcher_, mtc_tok, mtc_rep, mtc_bb, tt_flat, tt_delim,
+             token_tree};
+import earley_parser::{parse,leaf};
+import parse::lexer::{reader,new_tt_reader,tt_reader_as_reader};
+import parse::token::{token, w_ident, LBRACE, RBRACE};
+
+/* spans are ignored anyways */
+fn ms(m: matcher_) -> matcher {
+    {node: m, span: {lo: 0u, hi: 0u, expn_info: none}}
+}
+fn ttf(t: token) -> token_tree {
+    tt_flat({lo: 0u, hi: 0u, expn_info: none}, t)
+}
+
+fn expand_syntax_ext(cx: ext_ctxt, sp: codemap::span, body: ast::token_tree)
+    -> @ast::expr {
+
+    let body_core = alt body { tt_delim(tts) { tts } _ {fail}};
+    let tt_rdr = new_tt_reader(cx.parse_sess().span_diagnostic,
+                               cx.parse_sess().interner, body_core);
+    let args = parse(cx.parse_sess(), cx.cfg(), tt_rdr as reader,
+                     [ms(mtc_tok(LBRACE)),
+                      ms(mtc_bb(@"irrelevant", @"ident", 0u)),
+                      ms(mtc_tok(RBRACE))]);
+    let var = alt args[0u] { @leaf(w_ident(@name)) { name } _ { fail }};
+
+    alt os::getenv(var) {
+      option::none { ret make_new_str(cx, sp, ""); }
+      option::some(s) { ret make_new_str(cx, sp, s); }
+    }
+}
+
+fn make_new_str(cx: ext_ctxt, sp: codemap::span, +s: str) -> @ast::expr {
+    ret make_new_lit(cx, sp, ast::lit_str(@s));
+}
+//
+// Local Variables:
+// mode: rust
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// End:
+//
diff --git a/src/libsyntax/syntax.rc b/src/libsyntax/syntax.rc
index cf4d24b..7f9f872 100644
--- a/src/libsyntax/syntax.rc
+++ b/src/libsyntax/syntax.rc
@@ -75,4 +75,6 @@ mod ext {
     mod log_syntax;
     mod auto_serialize;
     mod source_util;
+
+    mod env2;
 }