Add mypy type tests

.travis.yml

@@ -12,5 +12,6 @@ script:
   - pip install -e .
   - py.test
   - mypy result/result.py
+  - mypy result/typetests.py
 after_success:
   - coveralls

README.rst

@@ -9,7 +9,8 @@ Result
     :alt: Coverage
     :target: https://coveralls.io/github/dbrgn/result
 
-A simple Result type for Python 3 `inspired by Rust <https://doc.rust-lang.org/std/result/>`__.
+A simple Result type for Python 3 `inspired by Rust
+<https://doc.rust-lang.org/std/result/>`__, fully type annotated.
 
 The idea is that a ``Result`` value can be either ``Ok(value)`` or ``Err(error)``,
 with a way to differentiate between the two. It will change code like this:
@@ -62,8 +63,8 @@ side, you don't have to return semantically unclear tuples anymore.
 
 Not all methods (https://doc.rust-lang.org/std/result/enum.Result.html) have
 been implemented, only the ones that make sense in the Python context. You still
-don't get any type safety, but some easier handling of types that can be OK or
-not, without resorting to custom exceptions.
+don't get any type safety at runtime, but some easier handling of types that can
+be OK or not, without resorting to custom exceptions.
 
 
 API

result/typetests.py

@@ -0,0 +1,12 @@
+from typing import List, Optional
+
+from .result import Result
+
+
+res1 = Result.Ok('hello')  # type: Result[str, int]
+if res1.is_ok():
+    ok = res1.ok()  # type: Optional[str]
+    mapped_to_float = res1.map_or(1.0, lambda s: len(s) * 1.5)  # type: float
+else:
+    err = res1.err()  # type: Optional[int]
+    mapped_to_list = res1.map_err(lambda e: [e]).err()  # type: Optional[List[int]]