diff --git a/src/comp/front/test.rs b/src/comp/front/test.rs
index b2c7b200babe..85e914cb0d98 100644
--- a/src/comp/front/test.rs
+++ b/src/comp/front/test.rs
@@ -92,7 +92,8 @@ fn fold_item(cx: &test_ctxt, i: &@ast::item, fld: fold::ast_fold) ->
    @ast::item {
 
     cx.path += [i.ident];
-    log #fmt["current path: %s", ast_util::path_name_i(cx.path)];
+    log #fmt["current path: %s",
+             istr::to_estr(ast_util::path_name_i(cx.path))];
 
     if is_test_fn(i) {
         log "this is a test function";
@@ -248,11 +249,11 @@ fn mk_test_desc_vec(cx: &test_ctxt) -> @ast::expr {
 fn mk_test_desc_rec(cx: &test_ctxt, test: test) -> @ast::expr {
     let path = test.path;
 
-    log #fmt["encoding %s", ast_util::path_name_i(path)];
+    log #fmt["encoding %s",
+             istr::to_estr(ast_util::path_name_i(path))];
 
     let name_lit: ast::lit =
-        nospan(ast::lit_str(
-            istr::from_estr(ast_util::path_name_i(path)), ast::sk_rc));
+        nospan(ast::lit_str(ast_util::path_name_i(path), ast::sk_rc));
     let name_expr: ast::expr =
         {id: cx.next_node_id(),
          node: ast::expr_lit(@name_lit),
diff --git a/src/comp/middle/alias.rs b/src/comp/middle/alias.rs
index 646913eafb46..7e517d6edef2 100644
--- a/src/comp/middle/alias.rs
+++ b/src/comp/middle/alias.rs
@@ -518,16 +518,18 @@ fn test_scope(cx: &ctx, sc: &scope, r: &restrict, p: &ast::path) {
         let msg =
             alt prob {
               overwritten(sp, wpt) {
-                {span: sp, msg: "overwriting " + ast_util::path_name(wpt)}
+                {span: sp, msg: "overwriting " +
+                    istr::to_estr(ast_util::path_name(wpt))}
               }
               val_taken(sp, vpt) {
                 {span: sp,
-                 msg: "taking the value of " + ast_util::path_name(vpt)}
+                 msg: "taking the value of " +
+                     istr::to_estr(ast_util::path_name(vpt))}
               }
             };
         cx.tcx.sess.span_err(msg.span,
                              msg.msg + " will invalidate alias " +
-                             ast_util::path_name(p) +
+                             istr::to_estr(ast_util::path_name(p)) +
                              ", which is still used");
     }
 }
diff --git a/src/comp/middle/resolve.rs b/src/comp/middle/resolve.rs
index 879a1f15dcc2..70c88cc005f1 100644
--- a/src/comp/middle/resolve.rs
+++ b/src/comp/middle/resolve.rs
@@ -324,7 +324,7 @@ fn resolve_names(e: &@env, c: &@ast::crate) {
               _ {
                 e.sess.span_err(p.span,
                                 "not a tag variant: " +
-                                ast_util::path_name(p));
+                                istr::to_estr(ast_util::path_name(p)));
               }
             }
           }
diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index a76626356655..a4f1c2c8102c 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -1792,10 +1792,10 @@ fn check_expr_with_unifier(fcx: &@fn_ctxt, expr: &@ast::expr, unify: &unifier,
             let binopstr = ast_util::binop_to_str(binop);
             let t_str = ty_to_str(fcx.ccx.tcx, resolved_t);
             let errmsg =
-                "binary operation " + binopstr +
-                    " cannot be applied to type `" +
-                istr::to_estr(t_str) + "`";
-            fcx.ccx.tcx.sess.span_err(span, errmsg);
+                ~"binary operation " + binopstr +
+                ~" cannot be applied to type `" +
+                t_str + ~"`";
+            fcx.ccx.tcx.sess.span_err(span, istr::to_estr(errmsg));
         }
     }
 
diff --git a/src/comp/syntax/ast_util.rs b/src/comp/syntax/ast_util.rs
index 72a633da9282..1aaa4c7a8f33 100644
--- a/src/comp/syntax/ast_util.rs
+++ b/src/comp/syntax/ast_util.rs
@@ -14,10 +14,10 @@ fn mk_sp(lo: uint, hi: uint) -> span {
 // make this a const, once the compiler supports it
 fn dummy_sp() -> span { ret mk_sp(0u, 0u); }
 
-fn path_name(p: &path) -> str { path_name_i(p.node.idents) }
+fn path_name(p: &path) -> istr { path_name_i(p.node.idents) }
 
-fn path_name_i(idents: &[ident]) -> str {
-    istr::to_estr(istr::connect(idents, ~"::"))
+fn path_name_i(idents: &[ident]) -> istr {
+    istr::connect(idents, ~"::")
 }
 
 fn local_def(id: node_id) -> def_id { ret {crate: local_crate, node: id}; }
@@ -83,27 +83,27 @@ fn pat_binding_ids(pat: &@pat) -> [node_id] {
     ret found;
 }
 
-fn binop_to_str(op: binop) -> str {
+fn binop_to_str(op: binop) -> istr {
     alt op {
-      add. { ret "+"; }
-      sub. { ret "-"; }
-      mul. { ret "*"; }
-      div. { ret "/"; }
-      rem. { ret "%"; }
-      and. { ret "&&"; }
-      or. { ret "||"; }
-      bitxor. { ret "^"; }
-      bitand. { ret "&"; }
-      bitor. { ret "|"; }
-      lsl. { ret "<<"; }
-      lsr. { ret ">>"; }
-      asr. { ret ">>>"; }
-      eq. { ret "=="; }
-      lt. { ret "<"; }
-      le. { ret "<="; }
-      ne. { ret "!="; }
-      ge. { ret ">="; }
-      gt. { ret ">"; }
+      add. { ret ~"+"; }
+      sub. { ret ~"-"; }
+      mul. { ret ~"*"; }
+      div. { ret ~"/"; }
+      rem. { ret ~"%"; }
+      and. { ret ~"&&"; }
+      or. { ret ~"||"; }
+      bitxor. { ret ~"^"; }
+      bitand. { ret ~"&"; }
+      bitor. { ret ~"|"; }
+      lsl. { ret ~"<<"; }
+      lsr. { ret ~">>"; }
+      asr. { ret ~">>>"; }
+      eq. { ret ~"=="; }
+      lt. { ret ~"<"; }
+      le. { ret ~"<="; }
+      ne. { ret ~"!="; }
+      ge. { ret ~">="; }
+      gt. { ret ~">"; }
     }
 }
 
@@ -111,12 +111,12 @@ pure fn lazy_binop(b: binop) -> bool {
     alt b { and. { true } or. { true } _ { false } }
 }
 
-fn unop_to_str(op: unop) -> str {
+fn unop_to_str(op: unop) -> istr {
     alt op {
-      box(mt) { if mt == mut { ret "@mutable "; } ret "@"; }
-      deref. { ret "*"; }
-      not. { ret "!"; }
-      neg. { ret "-"; }
+      box(mt) { if mt == mut { ret ~"@mutable "; } ret ~"@"; }
+      deref. { ret ~"*"; }
+      not. { ret ~"!"; }
+      neg. { ret ~"-"; }
     }
 }
 
@@ -124,18 +124,18 @@ fn is_path(e: &@expr) -> bool {
     ret alt e.node { expr_path(_) { true } _ { false } };
 }
 
-fn ty_mach_to_str(tm: ty_mach) -> str {
+fn ty_mach_to_str(tm: ty_mach) -> istr {
     alt tm {
-      ty_u8. { ret "u8"; }
-      ty_u16. { ret "u16"; }
-      ty_u32. { ret "u32"; }
-      ty_u64. { ret "u64"; }
-      ty_i8. { ret "i8"; }
-      ty_i16. { ret "i16"; }
-      ty_i32. { ret "i32"; }
-      ty_i64. { ret "i64"; }
-      ty_f32. { ret "f32"; }
-      ty_f64. { ret "f64"; }
+      ty_u8. { ret ~"u8"; }
+      ty_u16. { ret ~"u16"; }
+      ty_u32. { ret ~"u32"; }
+      ty_u64. { ret ~"u64"; }
+      ty_i8. { ret ~"i8"; }
+      ty_i16. { ret ~"i16"; }
+      ty_i32. { ret ~"i32"; }
+      ty_i64. { ret ~"i64"; }
+      ty_f32. { ret ~"f32"; }
+      ty_f64. { ret ~"f64"; }
     }
 }
 
diff --git a/src/comp/syntax/parse/token.rs b/src/comp/syntax/parse/token.rs
index bb678d26c7ef..b83a2f27e318 100644
--- a/src/comp/syntax/parse/token.rs
+++ b/src/comp/syntax/parse/token.rs
@@ -149,12 +149,12 @@ fn to_str(r: lexer::reader, t: token) -> istr {
       }
       LIT_UINT(u) { ret uint::to_str(u, 10u); }
       LIT_MACH_INT(tm, i) {
-        ret int::to_str(i, 10u) + ~"_" + istr::from_estr(ty_mach_to_str(tm));
+        ret int::to_str(i, 10u) + ~"_" + ty_mach_to_str(tm);
       }
       LIT_MACH_FLOAT(tm, s) {
         ret interner::get::<istr>(
             *r.get_interner(), s) + ~"_" +
-            istr::from_estr(ty_mach_to_str(tm));
+            ty_mach_to_str(tm);
       }
       LIT_FLOAT(s) {
         ret interner::get::<istr>(*r.get_interner(), s);
diff --git a/src/comp/syntax/print/pprust.rs b/src/comp/syntax/print/pprust.rs
index d98f1476b6bb..c01ede9d391f 100644
--- a/src/comp/syntax/print/pprust.rs
+++ b/src/comp/syntax/print/pprust.rs
@@ -276,7 +276,7 @@ fn print_type(s: &ps, ty: &@ast::ty) {
       ast::ty_uint. { word(s.s, ~"uint"); }
       ast::ty_float. { word(s.s, ~"float"); }
       ast::ty_machine(tm) {
-        word(s.s, istr::from_estr(ast_util::ty_mach_to_str(tm)));
+        word(s.s, ast_util::ty_mach_to_str(tm));
       }
       ast::ty_char. { word(s.s, ~"char"); }
       ast::ty_str. { word(s.s, ~"str"); }
@@ -846,11 +846,11 @@ fn print_expr(s: &ps, expr: &@ast::expr) {
         let prec = operator_prec(op);
         print_maybe_parens(s, lhs, prec);
         space(s.s);
-        word_space(s, istr::from_estr(ast_util::binop_to_str(op)));
+        word_space(s, ast_util::binop_to_str(op));
         print_maybe_parens(s, rhs, prec + 1);
       }
       ast::expr_unary(op, expr) {
-        word(s.s, istr::from_estr(ast_util::unop_to_str(op)));
+        word(s.s, ast_util::unop_to_str(op));
         print_maybe_parens(s, expr, parse::parser::unop_prec);
       }
       ast::expr_lit(lit) { print_literal(s, lit); }
@@ -982,7 +982,7 @@ fn print_expr(s: &ps, expr: &@ast::expr) {
       ast::expr_assign_op(op, lhs, rhs) {
         print_expr(s, lhs);
         space(s.s);
-        word(s.s, istr::from_estr(ast_util::binop_to_str(op)));
+        word(s.s, ast_util::binop_to_str(op));
         word_space(s, ~"=");
         print_expr(s, rhs);
       }
@@ -1526,12 +1526,12 @@ fn print_literal(s: &ps, lit: &@ast::lit) {
       ast::lit_float(fstr) { word(s.s, fstr); }
       ast::lit_mach_int(mach, val) {
         word(s.s, int::str(val as int));
-        word(s.s, istr::from_estr(ast_util::ty_mach_to_str(mach)));
+        word(s.s, ast_util::ty_mach_to_str(mach));
       }
       ast::lit_mach_float(mach, val) {
         // val is already a str
         word(s.s, val);
-        word(s.s, istr::from_estr(ast_util::ty_mach_to_str(mach)));
+        word(s.s, ast_util::ty_mach_to_str(mach));
       }
       ast::lit_nil. { word(s.s, ~"()"); }
       ast::lit_bool(val) {
diff --git a/src/comp/util/ppaux.rs b/src/comp/util/ppaux.rs
index 55dacf073a11..4ef7cfc60a88 100644
--- a/src/comp/util/ppaux.rs
+++ b/src/comp/util/ppaux.rs
@@ -114,7 +114,7 @@ fn ty_to_str(cx: &ctxt, typ: &t) -> istr {
           ty_int. { ~"int" }
           ty_float. { ~"float" }
           ty_uint. { ~"uint" }
-          ty_machine(tm) { istr::from_estr(ty_mach_to_str(tm)) }
+          ty_machine(tm) { ty_mach_to_str(tm) }
           ty_char. { ~"char" }
           ty_str. { ~"str" }
           ty_istr. { ~"istr" }