Add readme

Author: szabowexler

README.md

@@ -0,0 +1,88 @@
+# algebra
+Generic ADTs in Java.
+
+## Using
+
+To use `algebra` in your project simply include it in your POM:
+
+```xml
+    <dependency>
+      <groupId>com.hubspot</groupId>
+      <artifactId>algebra-public</artifactId>
+      <version>1.0</version>
+    </dependency>
+```
+
+## Provided Types
+
+The main type provided by `algebra` is the `Result<T, E>`. `T` and `E` can be any classes you want, but it is generally advisable that `E` be an enum or another ADT so you can correctly match on error conditions. Lets take a look at an example.
+
+```java
+enum Error {
+  BROKEN,
+  REALLY_BROKEN
+}
+
+public Result<String, Error> doWork() {
+  if (sucess) {
+    return Result.ok(result);
+  } else if (thing1Broke) {
+    return Result.err(Error.BROKEN);
+  }
+  
+  return Result.err(Error.REALLY_BROKEN);
+}
+```
+
+If we then want to use `doWork` in a library, but our library only has one error type, we can simply map the error and return a new result:
+
+```java
+
+enum LibError {
+  ERROR
+}
+
+public Result<String, LibError> doMoreWork() {
+  return doWork().mapErr(err -> LibError.ERROR);
+}
+```
+
+Of course when it gets to our client and they actually want to handle the error they can do so using `match`:
+
+```java
+client.doMoreWork().match(
+  err -> LOGGER.error("Got error: {}", err),
+  ok -> LOGGER.info("Got successful result: {}", ok)
+);
+```
+
+## Testing
+
+To test code with ADTs, we provide a fluent AssertJ API in `algebra-public-testing`.
+
+To use `algebra-public-testing` in your project simply include it in your POM:
+
+```xml
+    <dependency>
+      <groupId>com.hubspot</groupId>
+      <artifactId>algebra--public-testing</artifactId>
+      <version>1.0</version>
+      <scope>test</scope>
+    </dependency>
+```
+
+Add a static import and use the assertions:
+
+```java
+import static com.hubspot.assertj.algebra.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
+```
+
+```java
+  @Test
+  public void itWorks() {
+    assertThat(Result.ok("Ok"))
+        .isOk()
+        .containsOk("Ok");
+  }
+```