From e45ed323c99cf105b807ca79c5561570ec5c93c8 Mon Sep 17 00:00:00 2001
From: Erick Tryzelaar <erick.tryzelaar@gmail.com>
Date: Sat, 26 May 2012 20:33:08 -0700
Subject: [PATCH] Add methods iter, iter_err, map, map_err to the result type.

---
 src/libcore/result.rs | 134 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 134 insertions(+)

diff --git a/src/libcore/result.rs b/src/libcore/result.rs
index b0fad3192be..3c6622ba69d 100644
--- a/src/libcore/result.rs
+++ b/src/libcore/result.rs
@@ -107,6 +107,79 @@ fn chain_err<T: copy, U: copy, V: copy>(
     }
 }
 
+#[doc = "
+Call a function based on a previous result
+
+If `res` is `ok` then the value is extracted and passed to `op` whereupon
+`op`s result is returned. if `res` is `err` then it is immediately returned.
+This function can be used to compose the results of two functions.
+
+Example:
+
+    iter(read_file(file)) { |buf|
+        print_buf(buf)
+    }
+"]
+fn iter<T, E>(res: result<T, E>, f: fn(T)) {
+    alt res {
+      ok(t) { f(t) }
+      err(_) { }
+    }
+}
+
+#[doc = "
+Call a function based on a previous result
+
+If `res` is `err` then the value is extracted and passed to `op` whereupon
+`op`s result is returned. if `res` is `ok` then it is immediately returned.
+This function can be used to pass through a successful result while handling
+an error.
+"]
+fn iter_err<T, E>(res: result<T, E>, f: fn(E)) {
+    alt res {
+      ok(_) { }
+      err(e) { f(e) }
+    }
+}
+
+#[doc = "
+Call a function based on a previous result
+
+If `res` is `ok` then the value is extracted and passed to `op` whereupon
+`op`s result is wrapped in `ok` and returned. if `res` is `err` then it is
+immediately returned.  This function can be used to compose the results of two
+functions.
+
+Example:
+
+    let res = map(read_file(file)) { |buf|
+        parse_buf(buf)
+    }
+"]
+fn map<T, E: copy, U: copy>(res: result<T, E>, op: fn(T) -> U)
+  -> result<U, E> {
+    alt res {
+      ok(t) { ok(op(t)) }
+      err(e) { err(e) }
+    }
+}
+
+#[doc = "
+Call a function based on a previous result
+
+If `res` is `err` then the value is extracted and passed to `op` whereupon
+`op`s result is wrapped in an `err` and returned. if `res` is `ok` then it is
+immediately returned.  This function can be used to pass through a successful
+result while handling an error.
+"]
+fn map_err<T: copy, E, F: copy>(res: result<T, E>, op: fn(E) -> F)
+  -> result<T, F> {
+    alt res {
+      ok(t) { ok(t) }
+      err(e) { err(op(e)) }
+    }
+}
+
 impl extensions<T:copy, E:copy> for result<T,E> {
     fn get() -> T { get(self) }
 
@@ -123,6 +196,34 @@ impl extensions<T:copy, E:copy> for result<T,E> {
     fn chain_err<F:copy>(op: fn(E) -> result<T,F>) -> result<T,F> {
         chain_err(self, op)
     }
+
+    fn iter(f: fn(T)) {
+        alt self {
+          ok(t) { f(t) }
+          err(_) { }
+        }
+    }
+
+    fn iter_err(f: fn(E)) {
+        alt self {
+          ok(_) { }
+          err(e) { f(e) }
+        }
+    }
+
+    fn map<U:copy>(op: fn(T) -> U) -> result<U,E> {
+        alt self {
+          ok(t) { ok(op(t)) }
+          err(e) { err(e) }
+        }
+    }
+
+    fn map_err<F:copy>(op: fn(E) -> F) -> result<T,F> {
+        alt self {
+          ok(t) { ok(t) }
+          err(e) { err(op(e)) }
+        }
+    }
 }
 
 #[doc = "
@@ -248,4 +349,37 @@ mod tests {
     fn chain_failure() {
         assert get_err(chain(op3(), op2)) == "sadface";
     }
+
+    #[test]
+    fn test_impl_iter() {
+        let mut valid = false;
+        ok::<str, str>("a").iter { |_x| valid = true; };
+        assert valid;
+
+        err::<str, str>("b").iter { |_x| valid = false; };
+        assert valid;
+    }
+
+    #[test]
+    fn test_impl_iter_err() {
+        let mut valid = true;
+        ok::<str, str>("a").iter_err { |_x| valid = false; };
+        assert valid;
+
+        valid = false;
+        err::<str, str>("b").iter_err { |_x| valid = true; };
+        assert valid;
+    }
+
+    #[test]
+    fn test_impl_map() {
+        assert ok::<str, str>("a").map { |_x| "b" } == ok("b");
+        assert err::<str, str>("a").map { |_x| "b" } == err("a");
+    }
+
+    #[test]
+    fn test_impl_map_err() {
+        assert ok::<str, str>("a").map_err { |_x| "b" } == ok("a");
+        assert err::<str, str>("a").map_err { |_x| "b" } == err("b");
+    }
 }