std: added either::flip, to_result and result::to_either

Author: boggle

src/libcore/either.rs

@@ -78,6 +78,31 @@ fn partition<copy T, copy U>(eithers: [t<T, U>])
     ret {lefts: lefts, rights: rights};
 }
 
+/*
+Function: flip
+
+Flips between left and right of a given either
+*/
+pure fn flip<copy T, copy U>(eith: t<T, U>) -> t<U, T> {
+    alt eith {
+      right(r) { left(r) }
+      left(l) { right(l) }
+    }
+}
+
+/*
+Function: to_result
+
+Converts either::t to a result::t, making the "right" choice
+an ok result, and the "left" choice a fail
+*/
+pure fn to_result<copy T, copy U>(eith: t<T, U>) -> result::t<U, T> {
+    alt eith {
+      right(r) { result::ok(r) }
+      left(l) { result::err(l) }
+    }
+}
+
 //
 // Local Variables:
 // mode: rust

src/libcore/result.rs

@@ -42,7 +42,7 @@ fn get<T, U>(res: t<T, U>) -> T {
       ok(t) { t }
       err(_) {
         // FIXME: Serialize the error value
-        // and include it in the fail message
+        // and include it in the fail message (maybe just note it)
         fail "get called on error result";
       }
     }
@@ -71,7 +71,7 @@ Function: success
 
 Returns true if the result is <ok>
 */
-fn success<T, U>(res: t<T, U>) -> bool {
+pure fn success<T, U>(res: t<T, U>) -> bool {
     alt res {
       ok(_) { true }
       err(_) { false }
@@ -83,10 +83,17 @@ Function: failure
 
 Returns true if the result is <error>
 */
-fn failure<T, U>(res: t<T, U>) -> bool {
+pure fn failure<T, U>(res: t<T, U>) -> bool {
     !success(res)
 }
 
+pure fn to_either<copy T, copy U>(res: t<U, T>) -> either::t<T, U> {
+    alt res {
+      ok(res) { either::right(res) }
+      err(fail_) { either::left(fail_) }
+    }
+}
+
 /*
 Function: chain