Add more methods to Result. (FuelLabs#16)

* Add more methods to Result.

* Don't use catch all.

* Use catch up, but fix typo.

* Fix return type.

* Compile workarounds.

* fmt

* Remove todo comments.

* fmt

* Make Result public.

Forc.toml

@@ -4,6 +4,5 @@ entry = "lib.sw"
 license = "Apache-2.0"
 name = "lib-std"
 
-
 [dependencies]
 "core" = { git = "http://github.com/FuelLabs/sway-lib-core" }

src/result.sw

@@ -1,6 +1,52 @@
+//! Error handling with the `Result` type.
+//!
+//! [`Result<T, E>`][`Result`] is the type used for returning and propagating
+//! errors. It is an enum with the variants, [`Ok(T)`], representing
+//! success and containing a value, and [`Err(E)`], representing error
+//! and containing an error value.
+
 library result;
 
-enum Result<T, E> {
+/// `Result` is a type that represents either success ([`Ok`]) or failure
+/// ([`Err`]).
+pub enum Result<T, E> {
+    /// Contains the success value
     Ok: T,
+
+    /// Contains the error value
     Err: E,
 }
+
+/////////////////////////////////////////////////////////////////////////////
+// Type implementation
+/////////////////////////////////////////////////////////////////////////////
+
+impl Result<T, E> {
+    /////////////////////////////////////////////////////////////////////////
+    // Querying the contained values
+    /////////////////////////////////////////////////////////////////////////
+
+    /// Returns `true` if the result is [`Ok`].
+    fn is_ok(self) -> bool {
+        match self {
+            Result::Ok(T) => {
+                true
+            },
+            _ => {
+                false
+            },
+        }
+    }
+
+    /// Returns `true` if the result is [`Err`].
+    fn is_err(self) -> bool {
+        match self {
+            Result::Ok(T) => {
+                false
+            },
+            _ => {
+                true
+            },
+        }
+    }
+}