Add head and tail functions to std::ivec

They even have typestate preconditions

1 files changed, 10 insertions, 0 deletions

diff --git a/src/lib/ivec.rs b/src/lib/ivec.rs
index 25e1e0118e8..10f5e33505b 100644
--- a/src/lib/ivec.rs
+++ b/src/lib/ivec.rs
@@ -87,6 +87,16 @@ pred is_not_empty[T](&T[mutable?] v) -> bool {
 
 // Accessors
 
+/// Returns the first element of a vector
+fn head[T](&T[mutable?] v) : is_not_empty(v) -> T {
+    ret v.(0);
+}
+
+/// Returns all but the first element of a vector
+fn tail[T](&T[mutable?] v) : is_not_empty(v) -> T[mutable?] {
+    ret slice(v, 1u, len(v));
+}
+
 /// Returns the last element of `v`.
 fn last[T](&T[mutable?] v) -> option::t[T] {
     if (len(v) == 0u) { ret none; }