stdlib: Add vec::init. Returns all but the last element.

Per haskell, to go with head/tail, and last.

src/lib/vec.rs

@@ -193,10 +193,26 @@ fn tail<T>(v: [mutable? T]) : is_not_empty(v) -> [T] {
     ret slice(v, 1u, len(v));
 }
 
+// FIXME: This name is sort of confusing next to init_fn, etc
+// but this is the name haskell uses for this function,
+// along with head/tail/last.
+/*
+Function: init
+
+Returns all but the last elemnt of a vector
+
+Preconditions:
+`v` is not empty
+*/
+fn init<T>(v: [mutable? T]) -> [T] {
+    assert len(v) != 0u;
+    slice(v, 0u, len(v) - 1u)
+}
+
 /*
 Function: last
 
-Returns the last element of `v`
+Returns the last element of a vector
 
 Returns:
 

src/test/stdtest/vec.rs

@@ -5,6 +5,7 @@ import std::vec::*;
 import std::option;
 import std::option::none;
 import std::option::some;
+import std::task;
 
 fn square(n: uint) -> uint { ret n * n; }
 
@@ -443,6 +444,31 @@ fn reversed_mut() {
     assert (v2[1] == 10);
 }
 
+#[test]
+fn init() {
+    let v = vec::init([1, 2, 3]);
+    assert v == [1, 2];
+}
+
+#[cfg(target_os = "linux")]
+#[cfg(target_os = "mac")]
+#[test]
+fn init_empty() {
+
+    let r = task::join(
+        task::spawn_joinable((), fn (&&_i: ()) {
+            task::unsupervise();
+            vec::init::<int>([]);
+        }));
+    assert r == task::tr_failure
+}
+
+// FIXME: Windows can't undwind
+#[cfg(target_os = "win32")]
+#[test]
+#[ignore]
+fn init_empty() { }
+
 // Local Variables:
 // mode: rust;
 // fill-column: 78;