1 files changed, 60 insertions, 0 deletions
diff --git a/src/lib/Option.rs b/src/lib/Option.rs
new file mode 100644
index 00000000..3fb9aa3b
--- /dev/null
+++ b/src/lib/Option.rs
@@ -0,0 +1,60 @@
+// lib/Option.rs
+
+tag t[T] {
+    none;
+    some(T);
+}
+
+type operator[T, U] = fn(&T) -> U;
+
+fn get[T](&t[T] opt) -> T {
+    alt (opt) {
+        case (some[T](?x)) {
+            ret x;
+        }
+        case (none[T]) {
+            fail;
+        }
+    }
+    fail;   // FIXME: remove me when exhaustiveness checking works
+}
+
+fn map[T, U](&operator[T, U] f, &t[T] opt) -> t[U] {
+    alt (opt) {
+        case (some[T](?x)) {
+            ret some[U](f(x));
+        }
+        case (none[T]) {
+            ret none[U];
+        }
+    }
+    fail;   // FIXME: remove me when exhaustiveness checking works
+}
+
+fn is_none[T](&t[T] opt) -> bool {
+    alt (opt) {
+        case (none[T])      { ret true; }
+        case (some[T](_))   { ret false; }
+    }
+}
+
+fn from_maybe[T](&T def, &t[T] opt) -> T {
+    auto f = bind Util.id[T](_);
+    ret maybe[T, T](def, f, opt);
+}
+
+fn maybe[T, U](&U def, fn(&T) -> U f, &t[T] opt) -> U {
+    alt (opt) {
+        case (none[T]) { ret def; }
+        case (some[T](?t)) { ret f(t); }
+    }
+}
+// Local Variables:
+// mode: rust;
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+