diff --git a/src/comp/driver/session.rs b/src/comp/driver/session.rs
index 5a2b26739aae..1d892ed5b524 100644
--- a/src/comp/driver/session.rs
+++ b/src/comp/driver/session.rs
@@ -10,6 +10,7 @@ import std::option;
 import std::option::some;
 import std::option::none;
 import std::str;
+import std::istr;
 import syntax::parse::parser::parse_sess;
 
 tag os { os_win32; os_macos; os_linux; }
@@ -60,19 +61,19 @@ obj session(targ_cfg: @config,
     fn get_cstore() -> metadata::cstore::cstore { cstore }
     fn span_fatal(sp: span, msg: str) -> ! {
         // FIXME: Use constants, but rustboot doesn't know how to export them.
-        codemap::emit_error(some(sp), msg, parse_sess.cm);
+        codemap::emit_error(some(sp), istr::from_estr(msg), parse_sess.cm);
         fail;
     }
     fn fatal(msg: str) -> ! {
-        codemap::emit_error(none, msg, parse_sess.cm);
+        codemap::emit_error(none, istr::from_estr(msg), parse_sess.cm);
         fail;
     }
     fn span_err(sp: span, msg: str) {
-        codemap::emit_error(some(sp), msg, parse_sess.cm);
+        codemap::emit_error(some(sp), istr::from_estr(msg), parse_sess.cm);
         err_count += 1u;
     }
     fn err(msg: str) {
-        codemap::emit_error(none, msg, parse_sess.cm);
+        codemap::emit_error(none, istr::from_estr(msg), parse_sess.cm);
         err_count += 1u;
     }
     fn abort_if_errors() {
@@ -80,14 +81,18 @@ obj session(targ_cfg: @config,
     }
     fn span_warn(sp: span, msg: str) {
         // FIXME: Use constants, but rustboot doesn't know how to export them.
-        codemap::emit_warning(some(sp), msg, parse_sess.cm);
+        codemap::emit_warning(some(sp), istr::from_estr(msg), parse_sess.cm);
+    }
+    fn warn(msg: str) {
+        codemap::emit_warning(none, istr::from_estr(msg), parse_sess.cm);
     }
-    fn warn(msg: str) { codemap::emit_warning(none, msg, parse_sess.cm); }
     fn span_note(sp: span, msg: str) {
         // FIXME: Use constants, but rustboot doesn't know how to export them.
-        codemap::emit_note(some(sp), msg, parse_sess.cm);
+        codemap::emit_note(some(sp), istr::from_estr(msg), parse_sess.cm);
+    }
+    fn note(msg: str) {
+        codemap::emit_note(none, istr::from_estr(msg), parse_sess.cm);
     }
-    fn note(msg: str) { codemap::emit_note(none, msg, parse_sess.cm); }
     fn span_bug(sp: span, msg: str) -> ! {
         self.span_fatal(sp, #fmt["internal compiler error %s", msg]);
     }
@@ -107,7 +112,7 @@ obj session(targ_cfg: @config,
         ret syntax::parse::parser::next_node_id(parse_sess);
     }
     fn span_str(sp: span) -> str {
-        ret codemap::span_to_str(sp, self.get_codemap());
+        ret istr::to_estr(codemap::span_to_str(sp, self.get_codemap()));
     }
     fn set_main_id(d: node_id) { main_fn = some(d); }
     fn get_main_id() -> option::t<node_id> { main_fn }
diff --git a/src/comp/syntax/codemap.rs b/src/comp/syntax/codemap.rs
index 2ef4e3b2caa3..21ba2a98a773 100644
--- a/src/comp/syntax/codemap.rs
+++ b/src/comp/syntax/codemap.rs
@@ -73,26 +73,26 @@ tag opt_span {
 }
 type span = {lo: uint, hi: uint, expanded_from: opt_span};
 
-fn span_to_str(sp: &span, cm: &codemap) -> str {
+fn span_to_str(sp: &span, cm: &codemap) -> istr {
     let cur = sp;
-    let res = "";
+    let res = ~"";
     let prev_file = none;
     while true {
         let lo = lookup_char_pos(cm, cur.lo);
         let hi = lookup_char_pos(cm, cur.hi);
-        res +=
+        res += istr::from_estr(
             #fmt["%s:%u:%u: %u:%u",
                  if some(lo.filename) == prev_file {
                      "-"
                  } else {
                      istr::to_estr(lo.filename)
-                 }, lo.line, lo.col, hi.line, hi.col];
+                 }, lo.line, lo.col, hi.line, hi.col]);
         alt cur.expanded_from {
           os_none. { break; }
           os_some(new_sp) {
             cur = *new_sp;
             prev_file = some(lo.filename);
-            res += "<<";
+            res += ~"<<";
           }
         }
     }
@@ -100,24 +100,25 @@ fn span_to_str(sp: &span, cm: &codemap) -> str {
     ret res;
 }
 
-fn emit_diagnostic(sp: &option::t<span>, msg: &str, kind: &str, color: u8,
+fn emit_diagnostic(sp: &option::t<span>, msg: &istr, kind: &istr, color: u8,
                    cm: &codemap) {
-    let ss = "";
+    let ss = ~"";
     let maybe_lines: option::t<@file_lines> = none;
     alt sp {
       some(ssp) {
-        ss = span_to_str(ssp, cm) + " ";
+        ss = span_to_str(ssp, cm) + ~" ";
         maybe_lines = some(span_to_lines(ssp, cm));
       }
       none. { }
     }
-    io::stdout().write_str(istr::from_estr(ss));
+    io::stdout().write_str(ss);
     if term::color_supported() {
         term::fg(io::stdout().get_buf_writer(), color);
     }
-    io::stdout().write_str(istr::from_estr(#fmt["%s:", kind]));
+    io::stdout().write_str(istr::from_estr(#fmt["%s:", istr::to_estr(kind)]));
     if term::color_supported() { term::reset(io::stdout().get_buf_writer()); }
-    io::stdout().write_str(istr::from_estr(#fmt[" %s\n", msg]));
+    io::stdout().write_str(istr::from_estr(#fmt[" %s\n",
+                                                istr::to_estr(msg)]));
 
     maybe_highlight_lines(sp, cm, maybe_lines);
 }
@@ -129,12 +130,11 @@ fn maybe_highlight_lines(sp: &option::t<span>, cm: &codemap,
       some(lines) {
         // If we're not looking at a real file then we can't re-open it to
         // pull out the lines
-        if lines.name == "-" { ret; }
+        if lines.name == ~"-" { ret; }
 
         // FIXME: reading in the entire file is the worst possible way to
         //        get access to the necessary lines.
-        let file = istr::to_estr(
-            io::read_whole_file_str(istr::from_estr(lines.name)));
+        let file = io::read_whole_file_str(lines.name);
         let fm = get_filemap(cm, lines.name);
 
         // arbitrarily only print up to six lines of the error
@@ -151,8 +151,8 @@ fn maybe_highlight_lines(sp: &option::t<span>, cm: &codemap,
                 istr::from_estr(#fmt["%s:%u ",
                                      istr::to_estr(fm.name), line + 1u]));
             let s = get_line(fm, line as int, file);
-            if !str::ends_with(s, "\n") { s += "\n"; }
-            io::stdout().write_str(istr::from_estr(s));
+            if !istr::ends_with(s, ~"\n") { s += ~"\n"; }
+            io::stdout().write_str(s);
         }
         if elided {
             let last_line = display_lines[vec::len(display_lines) - 1u];
@@ -194,17 +194,17 @@ fn maybe_highlight_lines(sp: &option::t<span>, cm: &codemap,
     }
 }
 
-fn emit_warning(sp: &option::t<span>, msg: &str, cm: &codemap) {
-    emit_diagnostic(sp, msg, "warning", 11u8, cm);
+fn emit_warning(sp: &option::t<span>, msg: &istr, cm: &codemap) {
+    emit_diagnostic(sp, msg, ~"warning", 11u8, cm);
 }
-fn emit_error(sp: &option::t<span>, msg: &str, cm: &codemap) {
-    emit_diagnostic(sp, msg, "error", 9u8, cm);
+fn emit_error(sp: &option::t<span>, msg: &istr, cm: &codemap) {
+    emit_diagnostic(sp, msg, ~"error", 9u8, cm);
 }
-fn emit_note(sp: &option::t<span>, msg: &str, cm: &codemap) {
-    emit_diagnostic(sp, msg, "note", 10u8, cm);
+fn emit_note(sp: &option::t<span>, msg: &istr, cm: &codemap) {
+    emit_diagnostic(sp, msg, ~"note", 10u8, cm);
 }
 
-type file_lines = {name: str, lines: [uint]};
+type file_lines = {name: istr, lines: [uint]};
 
 fn span_to_lines(sp: span, cm: codemap::codemap) -> @file_lines {
     let lo = lookup_char_pos(cm, sp.lo);
@@ -213,10 +213,10 @@ fn span_to_lines(sp: span, cm: codemap::codemap) -> @file_lines {
     for each i: uint in uint::range(lo.line - 1u, hi.line as uint) {
         lines += [i];
     }
-    ret @{name: istr::to_estr(lo.filename), lines: lines};
+    ret @{name: lo.filename, lines: lines};
 }
 
-fn get_line(fm: filemap, line: int, file: &str) -> str {
+fn get_line(fm: filemap, line: int, file: &istr) -> istr {
     let begin: uint = fm.lines[line].byte - fm.start_pos.byte;
     let end: uint;
     if line as uint < vec::len(fm.lines) - 1u {
@@ -225,17 +225,17 @@ fn get_line(fm: filemap, line: int, file: &str) -> str {
         // If we're not done parsing the file, we're at the limit of what's
         // parsed. If we just slice the rest of the string, we'll print out
         // the remainder of the file, which is undesirable.
-        end = str::byte_len(file);
-        let rest = str::slice(file, begin, end);
-        let newline = str::index(rest, '\n' as u8);
+        end = istr::byte_len(file);
+        let rest = istr::slice(file, begin, end);
+        let newline = istr::index(rest, '\n' as u8);
         if newline != -1 { end = begin + (newline as uint); }
     }
-    ret str::slice(file, begin, end);
+    ret istr::slice(file, begin, end);
 }
 
-fn get_filemap(cm: codemap, filename: str) -> filemap {
+fn get_filemap(cm: codemap, filename: istr) -> filemap {
     for fm: filemap in cm.files {
-        if fm.name == istr::from_estr(filename) { ret fm; }
+        if fm.name == filename { ret fm; }
     }
     //XXjdm the following triggers a mismatched type bug
     //      (or expected function, found _|_)
diff --git a/src/comp/syntax/parse/lexer.rs b/src/comp/syntax/parse/lexer.rs
index d1cec447d9f6..988c46b6b88a 100644
--- a/src/comp/syntax/parse/lexer.rs
+++ b/src/comp/syntax/parse/lexer.rs
@@ -81,7 +81,7 @@ fn new_reader(cm: &codemap::codemap, src: &istr, filemap: codemap::filemap,
         fn err(m: &istr) {
             codemap::emit_error(
                 some(ast_util::mk_sp(chpos, chpos)),
-                istr::to_estr(m), cm);
+                m, cm);
         }
     }
     let strs: [istr] = [];
diff --git a/src/comp/syntax/parse/parser.rs b/src/comp/syntax/parse/parser.rs
index 288f11ad797c..0c4b6eac7b9a 100644
--- a/src/comp/syntax/parse/parser.rs
+++ b/src/comp/syntax/parse/parser.rs
@@ -113,12 +113,12 @@ fn new_parser(sess: parse_sess, cfg: ast::crate_cfg, rdr: lexer::reader,
         }
         fn fatal(m: &istr) -> ! {
             codemap::emit_error(some(self.get_span()),
-                                istr::to_estr(m), sess.cm);
+                                m, sess.cm);
             fail;
         }
         fn warn(m: &istr) {
             codemap::emit_warning(some(self.get_span()),
-                                  istr::to_estr(m), sess.cm);
+                                  m, sess.cm);
         }
         fn restrict(r: restriction) { restr = r; }
         fn get_restriction() -> restriction { ret restr; }
@@ -2581,8 +2581,8 @@ fn parse_crate_from_file(input: &istr, cfg: &ast::crate_cfg,
     } else if istr::ends_with(input, ~".rs") {
         parse_crate_from_source_file(input, cfg, sess)
     } else {
-        codemap::emit_error(none, "unknown input file type: "
-                            + istr::to_estr(input),
+        codemap::emit_error(none, ~"unknown input file type: "
+                            + input,
                             sess.cm);
         fail
     }