diff --git a/src/comp/syntax/parse/parser.rs b/src/comp/syntax/parse/parser.rs
index 4e393777d2a..3b2ba62ca93 100644
--- a/src/comp/syntax/parse/parser.rs
+++ b/src/comp/syntax/parse/parser.rs
@@ -746,8 +746,7 @@ fn parse_path_and_ty_param_substs(p: parser) -> ast::path {
 
 fn parse_mutability(p: parser) -> ast::mutability {
     if eat_word(p, "mutable") {
-        if p.peek() == token::QUES { p.bump(); ast::maybe_mut }
-        else { ast::mut }
+        ast::mut
     } else if eat_word(p, "const") {
         ast::maybe_mut
     } else {
diff --git a/src/comp/syntax/print/pprust.rs b/src/comp/syntax/print/pprust.rs
index e2d829f5217..f65ca2fbd57 100644
--- a/src/comp/syntax/print/pprust.rs
+++ b/src/comp/syntax/print/pprust.rs
@@ -1307,7 +1307,7 @@ fn print_op_maybe_parens(s: ps, expr: @ast::expr, outer_prec: int) {
 fn print_mutability(s: ps, mut: ast::mutability) {
     alt mut {
       ast::mut. { word_nbsp(s, "mutable"); }
-      ast::maybe_mut. { word_nbsp(s, "mutable?"); }
+      ast::maybe_mut. { word_nbsp(s, "const"); }
       ast::imm. {/* nothing */ }
     }
 }
diff --git a/src/comp/util/ppaux.rs b/src/comp/util/ppaux.rs
index b148b99cde8..fe899b8c59a 100644
--- a/src/comp/util/ppaux.rs
+++ b/src/comp/util/ppaux.rs
@@ -84,7 +84,7 @@ fn ty_to_str(cx: ctxt, typ: t) -> str {
         alt m.mut {
           ast::mut. { mstr = "mutable "; }
           ast::imm. { mstr = ""; }
-          ast::maybe_mut. { mstr = "mutable? "; }
+          ast::maybe_mut. { mstr = "const "; }
         }
         ret mstr + ty_to_str(cx, m.ty);
     }
diff --git a/src/lib/io.rs b/src/lib/io.rs
index 78a5384db13..e3ff7ee0995 100644
--- a/src/lib/io.rs
+++ b/src/lib/io.rs
@@ -188,7 +188,7 @@ fn file_reader(path: str) -> result::t<reader, str> {
 
 // Byte buffer readers
 
-// TODO: mutable? u8, but this fails with rustboot.
+// TODO: const u8, but this fails with rustboot.
 type byte_buf = @{buf: [u8], mutable pos: uint};
 
 obj byte_buf_reader(bbuf: byte_buf) {
diff --git a/src/lib/list.rs b/src/lib/list.rs
index 9ec762edd3d..6f51ab8e96c 100644
--- a/src/lib/list.rs
+++ b/src/lib/list.rs
@@ -25,7 +25,7 @@ Function: from_vec
 
 Create a list from a vector
 */
-fn from_vec<T>(v: [mutable? T]) -> list<T> {
+fn from_vec<T>(v: [const T]) -> list<T> {
     *vec::foldr({ |h, t| @cons(h, t) }, @nil::<T>, v)
 }
 
diff --git a/src/lib/sort.rs b/src/lib/sort.rs
index a4fe4cf3f8b..29c478472bd 100644
--- a/src/lib/sort.rs
+++ b/src/lib/sort.rs
@@ -20,7 +20,7 @@ Merge sort. Returns a new vector containing the sorted list.
 Has worst case O(n log n) performance, best case O(n), but
 is not space efficient. This is a stable sort.
 */
-fn merge_sort<T>(le: lteq<T>, v: [mutable? T]) -> [T] {
+fn merge_sort<T>(le: lteq<T>, v: [const T]) -> [T] {
     fn merge<T>(le: lteq<T>, a: [T], b: [T]) -> [T] {
         let rs: [T] = [];
         let a_len: uint = len::<T>(a);
diff --git a/src/lib/str.rs b/src/lib/str.rs
index 4184e8b2050..fb24c59f62f 100644
--- a/src/lib/str.rs
+++ b/src/lib/str.rs
@@ -189,7 +189,7 @@ Function: unsafe_from_bytes
 Converts a vector of bytes to a string. Does not verify that the
 vector contains valid UTF-8.
 */
-fn unsafe_from_bytes(v: [mutable? u8]) -> str unsafe {
+fn unsafe_from_bytes(v: [const u8]) -> str unsafe {
     let vcopy: [u8] = v + [0u8];
     let scopy: str = unsafe::reinterpret_cast(vcopy);
     unsafe::leak(vcopy);
diff --git a/src/lib/ufind.rs b/src/lib/ufind.rs
index d5d76d65ef4..7de70526a7f 100644
--- a/src/lib/ufind.rs
+++ b/src/lib/ufind.rs
@@ -44,7 +44,7 @@ fn set_count(ufnd: ufind) -> uint { ret vec::len::<node>(ufnd.nodes); }
 
 // Removes all sets with IDs greater than or equal to the given value.
 fn prune(ufnd: ufind, n: uint) {
-    // TODO: Use "slice" once we get rid of "mutable?"
+    // TODO: Use "slice" once we get rid of "const"
 
     let len = vec::len::<node>(ufnd.nodes);
     while len != n { vec::pop::<node>(ufnd.nodes); len -= 1u; }
diff --git a/src/lib/vec.rs b/src/lib/vec.rs
index 3d51560741b..cbe7f2cf8b3 100644
--- a/src/lib/vec.rs
+++ b/src/lib/vec.rs
@@ -8,13 +8,13 @@ import ptr::addr_of;
 
 #[abi = "rust-intrinsic"]
 native mod rusti {
-    fn vec_len<T>(&&v: [mutable? T]) -> uint;
+    fn vec_len<T>(&&v: [const T]) -> uint;
 }
 
 #[abi = "cdecl"]
 native mod rustrt {
     fn vec_reserve_shared<T>(t: *sys::type_desc,
-                             &v: [mutable? T],
+                             &v: [const T],
                              n: uint);
     fn vec_from_buf_shared<T>(t: *sys::type_desc,
                               ptr: *T,
@@ -34,7 +34,7 @@ Predicate: is_empty
 
 Returns true if a vector contains no elements.
 */
-pure fn is_empty<T>(v: [mutable? T]) -> bool {
+pure fn is_empty<T>(v: [const T]) -> bool {
     // FIXME: This would be easier if we could just call len
     for t: T in v { ret false; }
     ret true;
@@ -45,7 +45,7 @@ Predicate: is_not_empty
 
 Returns true if a vector contains some elements.
 */
-pure fn is_not_empty<T>(v: [mutable? T]) -> bool { ret !is_empty(v); }
+pure fn is_not_empty<T>(v: [const T]) -> bool { ret !is_empty(v); }
 
 /*
 Predicate: same_length
@@ -69,7 +69,7 @@ Parameters:
 v - A vector
 n - The number of elements to reserve space for
 */
-fn reserve<T>(&v: [mutable? T], n: uint) {
+fn reserve<T>(&v: [const T], n: uint) {
     rustrt::vec_reserve_shared(sys::get_type_desc::<T>(), v, n);
 }
 
@@ -78,7 +78,7 @@ Function: len
 
 Returns the length of a vector
 */
-pure fn len<T>(v: [mutable? T]) -> uint { unchecked { rusti::vec_len(v) } }
+pure fn len<T>(v: [const T]) -> uint { unchecked { rusti::vec_len(v) } }
 
 /*
 Function: init_fn
@@ -181,7 +181,7 @@ Returns the first element of a vector
 Predicates:
 <is_not_empty> (v)
 */
-fn head<T>(v: [mutable? T]) : is_not_empty(v) -> T { ret v[0]; }
+fn head<T>(v: [const T]) : is_not_empty(v) -> T { ret v[0]; }
 
 /*
 Function: tail
@@ -191,7 +191,7 @@ Returns all but the first element of a vector
 Predicates:
 <is_not_empty> (v)
 */
-fn tail<T>(v: [mutable? T]) : is_not_empty(v) -> [T] {
+fn tail<T>(v: [const T]) : is_not_empty(v) -> [T] {
     ret slice(v, 1u, len(v));
 }
 
@@ -206,7 +206,7 @@ Returns all but the last elemnt of a vector
 Preconditions:
 `v` is not empty
 */
-fn init<T>(v: [mutable? T]) -> [T] {
+fn init<T>(v: [const T]) -> [T] {
     assert len(v) != 0u;
     slice(v, 0u, len(v) - 1u)
 }
@@ -221,7 +221,7 @@ Returns:
 An option containing the last element of `v` if `v` is not empty, or
 none if `v` is empty.
 */
-fn last<T>(v: [mutable? T]) -> option::t<T> {
+fn last<T>(v: [const T]) -> option::t<T> {
     if len(v) == 0u { ret none; }
     ret some(v[len(v) - 1u]);
 }
@@ -234,7 +234,7 @@ Returns the last element of a non-empty vector `v`
 Predicates:
 <is_not_empty> (v)
 */
-fn last_total<T>(v: [mutable? T]) : is_not_empty(v) -> T {
+fn last_total<T>(v: [const T]) : is_not_empty(v) -> T {
     ret v[len(v) - 1u];
 }
 
@@ -243,7 +243,7 @@ Function: slice
 
 Returns a copy of the elements from [`start`..`end`) from `v`.
 */
-fn slice<T>(v: [mutable? T], start: uint, end: uint) -> [T] {
+fn slice<T>(v: [const T], start: uint, end: uint) -> [T] {
     assert (start <= end);
     assert (end <= len(v));
     let result = [];
@@ -259,7 +259,7 @@ Function: slice_mut
 
 Returns a copy of the elements from [`start`..`end`) from `v`.
 */
-fn slice_mut<T>(v: [mutable? T], start: uint, end: uint) -> [mutable T] {
+fn slice_mut<T>(v: [const T], start: uint, end: uint) -> [mutable T] {
     assert (start <= end);
     assert (end <= len(v));
     let result = [mutable];
@@ -277,7 +277,7 @@ Function: shift
 
 Removes the first element from a vector and return it
 */
-fn shift<T>(&v: [mutable? T]) -> T {
+fn shift<T>(&v: [const T]) -> T {
     let ln = len::<T>(v);
     assert (ln > 0u);
     let e = v[0];
@@ -291,7 +291,7 @@ Function: pop
 
 Remove the last element from a vector and return it
 */
-fn pop<T>(&v: [mutable? T]) -> T {
+fn pop<T>(&v: [const T]) -> T {
     let ln = len(v);
     assert (ln > 0u);
     ln -= 1u;
@@ -323,7 +323,7 @@ fn grow<T>(&v: [T], n: uint, initval: T) {
 }
 
 // TODO: Remove me once we have slots.
-// FIXME: Can't grow take a [mutable? T]
+// FIXME: Can't grow take a [const T]
 /*
 Function: grow_mut
 
@@ -384,7 +384,7 @@ Function: map
 
 Apply a function to each element of a vector and return the results
 */
-fn map<T, U>(f: block(T) -> U, v: [mutable? T]) -> [U] {
+fn map<T, U>(f: block(T) -> U, v: [const T]) -> [U] {
     let result = [];
     reserve(result, len(v));
     for elem: T in v {
@@ -416,7 +416,7 @@ Apply a function to each element of a vector and return the results
 If function `f` returns `none` then that element is excluded from
 the resulting vector.
 */
-fn filter_map<T, U>(f: block(T) -> option::t<U>, v: [mutable? T]) -> [U] {
+fn filter_map<T, U>(f: block(T) -> option::t<U>, v: [const T]) -> [U] {
     let result = [];
     for elem: T in v {
         let elem2 = elem; // satisfies alias checker
@@ -437,7 +437,7 @@ holds.
 Apply function `f` to each element of `v` and return a vector containing
 only those elements for which `f` returned true.
 */
-fn filter<T>(f: block(T) -> bool, v: [mutable? T]) -> [T] {
+fn filter<T>(f: block(T) -> bool, v: [const T]) -> [T] {
     let result = [];
     for elem: T in v {
         let elem2 = elem; // satisfies alias checker
@@ -454,7 +454,7 @@ Function: concat
 Concatenate a vector of vectors. Flattens a vector of vectors of T into
 a single vector of T.
 */
-fn concat<T>(v: [mutable? [mutable? T]]) -> [T] {
+fn concat<T>(v: [const [const T]]) -> [T] {
     // FIXME: So much copying
     let new: [T] = [];
     for inner: [T] in v { new += inner; }
@@ -466,7 +466,7 @@ Function: foldl
 
 Reduce a vector from left to right
 */
-fn foldl<T, U>(p: block(T, U) -> T, z: T, v: [mutable? U]) -> T {
+fn foldl<T, U>(p: block(T, U) -> T, z: T, v: [const U]) -> T {
     let accum = z;
     iter(v) { |elt|
         accum = p(accum, elt);
@@ -479,7 +479,7 @@ Function: foldr
 
 Reduce a vector from right to left
 */
-fn foldr<T, U>(p: block(T, U) -> U, z: U, v: [mutable? T]) -> U {
+fn foldr<T, U>(p: block(T, U) -> U, z: U, v: [const T]) -> U {
     let accum = z;
     riter(v) { |elt|
         accum = p(elt, accum);
@@ -526,7 +526,7 @@ Function: count
 
 Returns the number of elements that are equal to a given value
 */
-fn count<T>(x: T, v: [mutable? T]) -> uint {
+fn count<T>(x: T, v: [const T]) -> uint {
     let cnt = 0u;
     for elt: T in v { if x == elt { cnt += 1u; } }
     ret cnt;
@@ -646,7 +646,7 @@ Function: reversed
 
 Returns a vector with the order of elements reversed
 */
-fn reversed<T>(v: [mutable? T]) -> [T] {
+fn reversed<T>(v: [const T]) -> [T] {
     let rs: [T] = [];
     let i = len::<T>(v);
     if i == 0u { ret rs; } else { i -= 1u; }
@@ -690,7 +690,7 @@ Iterates over vector `v` and, for each element, calls function `f` with the
 element's value.
 
 */
-fn iter<T>(v: [mutable? T], f: block(T)) {
+fn iter<T>(v: [const T], f: block(T)) {
     iter2(v) { |_i, v| f(v) }
 }
 
@@ -702,7 +702,7 @@ Iterates over a vector's elements and indexes
 Iterates over vector `v` and, for each element, calls function `f` with the
 element's value and index.
 */
-fn iter2<T>(v: [mutable? T], f: block(uint, T)) {
+fn iter2<T>(v: [const T], f: block(uint, T)) {
     let i = 0u;
     for x in v { f(i, x); i += 1u; }
 }
@@ -716,7 +716,7 @@ Iterates over vector `v` and, for each element, calls function `f` with the
 element's value.
 
 */
-fn riter<T>(v: [mutable? T], f: block(T)) {
+fn riter<T>(v: [const T], f: block(T)) {
     riter2(v) { |_i, v| f(v) }
 }
 
@@ -728,7 +728,7 @@ Iterates over a vector's elements and indexes in reverse
 Iterates over vector `v` and, for each element, calls function `f` with the
 element's value and index.
 */
-fn riter2<T>(v: [mutable? T], f: block(uint, T)) {
+fn riter2<T>(v: [const T], f: block(uint, T)) {
     let i = len(v);
     while 0u < i {
         i -= 1u;
@@ -746,7 +746,7 @@ is sorted then the permutations are lexicographically sorted).
 The total number of permutations produced is `len(v)!`.  If `v` contains
 repeated elements, then some permutations are repeated.
 */
-fn permute<T>(v: [mutable? T], put: block([T])) {
+fn permute<T>(v: [const T], put: block([T])) {
   let ln = len(v);
   if ln == 0u {
     put([]);
@@ -798,7 +798,7 @@ mod unsafe {
     modifing its buffers, so it is up to the caller to ensure that
     the vector is actually the specified size.
     */
-    unsafe fn set_len<T>(&v: [mutable? T], new_len: uint) {
+    unsafe fn set_len<T>(&v: [const T], new_len: uint) {
         let repr: **vec_repr = ::unsafe::reinterpret_cast(addr_of(v));
         (**repr).fill = new_len * sys::size_of::<T>();
     }
@@ -814,7 +814,7 @@ mod unsafe {
     Modifying the vector may cause its buffer to be reallocated, which
     would also make any pointers to it invalid.
     */
-    unsafe fn to_ptr<T>(v: [mutable? T]) -> *T {
+    unsafe fn to_ptr<T>(v: [const T]) -> *T {
         let repr: **vec_repr = ::unsafe::reinterpret_cast(addr_of(v));
         ret ::unsafe::reinterpret_cast(addr_of((**repr).data));
     }
diff --git a/src/test/compile-fail/mutable-huh-box-assign.rs b/src/test/compile-fail/mutable-huh-box-assign.rs
index 9a3b35a47c6..1f06a82f9a6 100644
--- a/src/test/compile-fail/mutable-huh-box-assign.rs
+++ b/src/test/compile-fail/mutable-huh-box-assign.rs
@@ -1,7 +1,7 @@
 // error-pattern: assigning to immutable box
 
 fn main() {
-    fn f(&&v: @mutable? int) {
+    fn f(&&v: @const int) {
         // This shouldn't be possible
         *v = 1
     }
diff --git a/src/test/compile-fail/mutable-huh-field-assign.rs b/src/test/compile-fail/mutable-huh-field-assign.rs
index e6535c43f01..0aee89fb630 100644
--- a/src/test/compile-fail/mutable-huh-field-assign.rs
+++ b/src/test/compile-fail/mutable-huh-field-assign.rs
@@ -1,7 +1,7 @@
 // error-pattern: assigning to immutable field
 
 fn main() {
-    fn f(&&v: {mutable? field: int}) {
+    fn f(&&v: {const field: int}) {
         // This shouldn't be possible
         v.field = 1
     }
diff --git a/src/test/compile-fail/mutable-huh-ptr-assign.rs b/src/test/compile-fail/mutable-huh-ptr-assign.rs
index fdd2cbb9705..46f1ceee15d 100644
--- a/src/test/compile-fail/mutable-huh-ptr-assign.rs
+++ b/src/test/compile-fail/mutable-huh-ptr-assign.rs
@@ -3,7 +3,7 @@
 use std;
 
 fn main() {
-    unsafe fn f(&&v: *mutable? int) {
+    unsafe fn f(&&v: *const int) {
         // This shouldn't be possible
         *v = 1
     }
diff --git a/src/test/compile-fail/mutable-huh-unique-assign.rs b/src/test/compile-fail/mutable-huh-unique-assign.rs
index deb6adfb06c..6a0d81ca50b 100644
--- a/src/test/compile-fail/mutable-huh-unique-assign.rs
+++ b/src/test/compile-fail/mutable-huh-unique-assign.rs
@@ -1,7 +1,7 @@
 // error-pattern: assigning to immutable box
 
 fn main() {
-    fn f(&&v: ~mutable? int) {
+    fn f(&&v: ~const int) {
         // This shouldn't be possible
         *v = 1
     }
diff --git a/src/test/compile-fail/mutable-huh-variance-box.rs b/src/test/compile-fail/mutable-huh-variance-box.rs
index 72732a5d0b2..1715acc5859 100644
--- a/src/test/compile-fail/mutable-huh-variance-box.rs
+++ b/src/test/compile-fail/mutable-huh-variance-box.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = @mutable [0];
 
-    fn f(&&v: @mutable [mutable? int]) {
+    fn f(&&v: @mutable [const int]) {
         *v = [mutable 3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-variance-deep.rs b/src/test/compile-fail/mutable-huh-variance-deep.rs
index aafe0f1465d..072a1f04c8b 100644
--- a/src/test/compile-fail/mutable-huh-variance-deep.rs
+++ b/src/test/compile-fail/mutable-huh-variance-deep.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = [mutable @mutable ~mutable [0]];
 
-    fn f(&&v: [mutable @mutable ~mutable [mutable? int]]) {
+    fn f(&&v: [mutable @mutable ~mutable [const int]]) {
     }
 
     f(v);
diff --git a/src/test/compile-fail/mutable-huh-variance-ptr.rs b/src/test/compile-fail/mutable-huh-variance-ptr.rs
index 8f19ebd1dff..0cb05af444c 100644
--- a/src/test/compile-fail/mutable-huh-variance-ptr.rs
+++ b/src/test/compile-fail/mutable-huh-variance-ptr.rs
@@ -6,7 +6,7 @@ fn main() {
     let a = [0];
     let v: *mutable [int] = std::ptr::mut_addr_of(a);
 
-    fn f(&&v: *mutable [mutable? int]) {
+    fn f(&&v: *mutable [const int]) {
         unsafe {
             *v = [mutable 3]
         }
diff --git a/src/test/compile-fail/mutable-huh-variance-rec.rs b/src/test/compile-fail/mutable-huh-variance-rec.rs
index 2225eb5c364..3bd079ba6ff 100644
--- a/src/test/compile-fail/mutable-huh-variance-rec.rs
+++ b/src/test/compile-fail/mutable-huh-variance-rec.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = {mutable g: [0]};
 
-    fn f(&&v: {mutable g: [mutable? int]}) {
+    fn f(&&v: {mutable g: [const int]}) {
         v.g = [mutable 3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-variance-unique.rs b/src/test/compile-fail/mutable-huh-variance-unique.rs
index ca3751629e3..54ffccecaf0 100644
--- a/src/test/compile-fail/mutable-huh-variance-unique.rs
+++ b/src/test/compile-fail/mutable-huh-variance-unique.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = ~mutable [0];
 
-    fn f(&&v: ~mutable [mutable? int]) {
+    fn f(&&v: ~mutable [const int]) {
         *v = [mutable 3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-variance-vec1.rs b/src/test/compile-fail/mutable-huh-variance-vec1.rs
index 0b834ab59d3..e688fe2c26e 100644
--- a/src/test/compile-fail/mutable-huh-variance-vec1.rs
+++ b/src/test/compile-fail/mutable-huh-variance-vec1.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = [mutable [0]];
 
-    fn f(&&v: [mutable [mutable? int]]) {
+    fn f(&&v: [mutable [const int]]) {
         v[0] = [mutable 3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-variance-vec2.rs b/src/test/compile-fail/mutable-huh-variance-vec2.rs
index c3b5c36d1d1..81422f047f4 100644
--- a/src/test/compile-fail/mutable-huh-variance-vec2.rs
+++ b/src/test/compile-fail/mutable-huh-variance-vec2.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = [mutable [mutable 0]];
 
-    fn f(&&v: [mutable [mutable? int]]) {
+    fn f(&&v: [mutable [const int]]) {
         v[0] = [3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-variance-vec3.rs b/src/test/compile-fail/mutable-huh-variance-vec3.rs
index dff3c1173fe..ef5da13a3af 100644
--- a/src/test/compile-fail/mutable-huh-variance-vec3.rs
+++ b/src/test/compile-fail/mutable-huh-variance-vec3.rs
@@ -3,7 +3,7 @@
 fn main() {
     let v = [mutable [mutable [0]]];
 
-    fn f(&&v: [mutable [mutable [mutable? int]]]) {
+    fn f(&&v: [mutable [mutable [const int]]]) {
         v[0][1] = [mutable 3]
     }
 
diff --git a/src/test/compile-fail/mutable-huh-vec-assign.rs b/src/test/compile-fail/mutable-huh-vec-assign.rs
index 1f273d376f1..43738008ec6 100644
--- a/src/test/compile-fail/mutable-huh-vec-assign.rs
+++ b/src/test/compile-fail/mutable-huh-vec-assign.rs
@@ -1,7 +1,7 @@
 // error-pattern: assigning to immutable vec content
 
 fn main() {
-    fn f(&&v: [mutable? int]) {
+    fn f(&&v: [const int]) {
         // This shouldn't be possible
         v[0] = 1
     }
diff --git a/src/test/run-pass/vec-push.rs b/src/test/run-pass/vec-push.rs
index 0e0d828bf63..8cdd5e82f18 100644
--- a/src/test/run-pass/vec-push.rs
+++ b/src/test/run-pass/vec-push.rs
@@ -1,5 +1,5 @@
 
 
-fn push<T>(&v: [mutable? T], t: T) { v += [t]; }
+fn push<T>(&v: [const T], t: T) { v += [t]; }
 
 fn main() { let v = [1, 2, 3]; push(v, 1); }