diff --git a/src/libcore/bool.rs b/src/libcore/bool.rs
index 0fc869d1b41..af4b752f4dd 100644
--- a/src/libcore/bool.rs
+++ b/src/libcore/bool.rs
@@ -123,7 +123,7 @@ Returns:
 
 An u8 whose first bit is set if `if_true(v)` holds
 */
-fn to_bit(v: t) -> u8 { if v { 1u8 } else { 0u8 } }
+pure fn to_bit(v: t) -> u8 { if v { 1u8 } else { 0u8 } }
 
 // Local Variables:
 // mode: rust;
diff --git a/src/libcore/box.rs b/src/libcore/box.rs
index 6682fe17284..23b5889bc6a 100644
--- a/src/libcore/box.rs
+++ b/src/libcore/box.rs
@@ -10,7 +10,7 @@ Function: ptr_eq
 
 Determine if two shared boxes point to the same object
 */
-fn ptr_eq<T>(a: @T, b: @T) -> bool {
+pure fn ptr_eq<T>(a: @T, b: @T) -> bool {
     // FIXME: ptr::addr_of
     unsafe {
         let a_ptr: uint = unsafe::reinterpret_cast(a);
diff --git a/src/libcore/char.rs b/src/libcore/char.rs
index 5ff7681ae8a..2648c8481df 100644
--- a/src/libcore/char.rs
+++ b/src/libcore/char.rs
@@ -122,7 +122,7 @@ pure fn to_digit(c: char) -> u8 unsafe {
  Convert a char to the corresponding digit. Returns none when the
  character is not a valid hexadecimal digit.
 */
-fn maybe_digit(c: char) -> option::t<u8> {
+pure fn maybe_digit(c: char) -> option::t<u8> {
     alt c {
       '0' to '9' { option::some(c as u8 - ('0' as u8)) }
       'a' to 'z' { option::some(c as u8 + 10u8 - ('a' as u8)) }
@@ -143,7 +143,7 @@ fn maybe_digit(c: char) -> option::t<u8> {
  Returns:
   -1 if a<b, 0 if a==b, +1 if a>b
 */
-fn cmp(a: char, b: char) -> int {
+pure fn cmp(a: char, b: char) -> int {
     ret  if b > a { -1 }
     else if b < a { 1 }
     else { 0 }
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 403cb47f47e..39e68a01519 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -30,7 +30,7 @@ Failure:
 
 Fails if the value equals `none`.
 */
-fn get<copy T>(opt: t<T>) -> T {
+pure fn get<copy T>(opt: t<T>) -> T {
     alt opt { some(x) { ret x; } none. { fail "option none"; } }
 }
 
@@ -61,7 +61,7 @@ Function: from_maybe
 
 Returns the contained value or a default
 */
-fn from_maybe<T>(def: T, opt: t<T>) -> T {
+pure fn from_maybe<T>(def: T, opt: t<T>) -> T {
     alt opt { some(x) { x } none. { def } }
 }
 
diff --git a/src/libcore/str.rs b/src/libcore/str.rs
index 8a532fcc753..802297223e9 100644
--- a/src/libcore/str.rs
+++ b/src/libcore/str.rs
@@ -26,14 +26,14 @@ Function: eq
 
 Bytewise string equality
 */
-fn eq(&&a: str, &&b: str) -> bool { a == b }
+pure fn eq(&&a: str, &&b: str) -> bool { a == b }
 
 /*
 Function: lteq
 
 Bytewise less than or equal
 */
-fn lteq(&&a: str, &&b: str) -> bool { a <= b }
+pure fn lteq(&&a: str, &&b: str) -> bool { a <= b }
 
 /*
 Function: hash
@@ -131,7 +131,7 @@ Function: byte_len
 
 Returns the length in bytes of a string
 */
-fn byte_len(s: str) -> uint unsafe {
+pure fn byte_len(s: str) -> uint unsafe {
     let v: [u8] = unsafe::reinterpret_cast(s);
     let vlen = vec::len(v);
     unsafe::leak(v);
@@ -261,7 +261,7 @@ Function: utf8_char_width
 
 FIXME: What does this function do?
 */
-fn utf8_char_width(b: u8) -> uint {
+pure fn utf8_char_width(b: u8) -> uint {
     let byte: uint = b as uint;
     if byte < 128u { ret 1u; }
     if byte < 192u {
diff --git a/src/libcore/sys.rs b/src/libcore/sys.rs
index 3b4a3b8c643..9c8b0972111 100644
--- a/src/libcore/sys.rs
+++ b/src/libcore/sys.rs
@@ -42,7 +42,7 @@ Function: last_os_error
 Get a string representing the platform-dependent last error
 */
 fn last_os_error() -> str {
-    ret rustrt::last_os_error();
+    rustrt::last_os_error()
 }
 
 /*
diff --git a/src/libcore/vec.rs b/src/libcore/vec.rs
index d8f89b3b27b..d056eb8d04d 100644
--- a/src/libcore/vec.rs
+++ b/src/libcore/vec.rs
@@ -181,7 +181,7 @@ Returns the first element of a vector
 Predicates:
 <is_not_empty> (v)
 */
-fn head<copy T>(v: [const T]) : is_not_empty(v) -> T { ret v[0]; }
+pure fn head<copy T>(v: [const T]) : is_not_empty(v) -> T { ret v[0]; }
 
 /*
 Function: tail
@@ -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<copy T>(v: [const T]) -> option::t<T> {
+pure fn last<copy 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<copy T>(v: [const T]) : is_not_empty(v) -> T {
+pure fn last_total<copy T>(v: [const T]) : is_not_empty(v) -> T {
     ret v[len(v) - 1u];
 }