Add usage example to README

README.md

@@ -6,6 +6,94 @@ the following features are included:
 - [`Maybe` data type](./include/Maybe.h)
 - [`Either` data type](./include/Either.h)
 
+## Installation
+
+Simply add the [`include`](./include) folder as a dependency to your project and
+include the main header file:
+
+```c
+#include <Func.h>
+```
+
+## Usage
+
+### Maybe
+
+A Maybe type is a polymorphic type that represents encapsulation of an optional
+value.
+
+The type can be used like this:
+
+```c
+#include "include/Func.h"
+
+MAYBE(int, foo);
+
+int main(void) {
+    Maybe(foo) maybeFoo = Just(foo, 2);
+
+    /* check if the Maybe value contains nothing */
+    if (isNothing(maybeFoo)) {
+        /* wont be executed */
+    }
+
+    /* check if the Maybe value contains something */
+    if (isJust(maybeFoo)) {
+        /* will be executed */
+    }
+
+    /* Extract the content to `t` */
+    int t = 0;
+    fromJust(maybeFoo, t);
+
+    /* t will be `2` now */
+
+    return 0;
+}
+```
+
+### Either
+
+The Either type represents values with two possibilities: a value of type Either
+a b is either Left a or Right b.
+
+The Either type is sometimes used to represent a value which is either correct
+or an error; by convention, the Left constructor is used to hold an error value
+and the Right constructor is used to hold a correct value (mnemonic: "right"
+also means "correct").
+
+```c
+#include "include/Func.h"
+
+EITHER(int, foo, char, bar);
+
+int main(void) {
+    Either(foo, bar) eitherFooOrBar = Right(foo, bar, 'a');
+
+    if (isLeft(eitherFooOrBar)) {
+        /* wont be executed */
+    }
+
+    if (isRight(eitherFooOrBar)) {
+        /* will be executed */
+    }
+
+    /* Try to extract the Left content to `x` */
+    char x = 1;
+    fromLeft(eitherFooOrBar, x);
+
+    /* x will remain '1' */
+
+    /* Try to extract the Right content to `y` */
+    char y = ' ';
+    fromRight(eitherFooOrBar, y);
+
+    /* y will be 'a' now */
+
+    return 0;
+}
+```
+
 ## Contributing
 You want to contribute to this project? Wow, thanks! So please just fork it and
 send me a pull request.

include/Either.h

@@ -37,9 +37,10 @@
 /**
  * @brief Creates a new named 'Either'
  */
-#define EITHER(a, b, n) \
-    typedef t n;        \
-    EITHER_TYPE(a, b)
+#define EITHER(a, b, c, d) \
+    typedef a b;           \
+    typedef c d;           \
+    EITHER_TYPE(b, d)
 
 /**
  * @brief Check if the Either contains Left data

include/Func.h

@@ -3,6 +3,10 @@
 #ifndef INCLUDE_FUNC_H_
 #define INCLUDE_FUNC_H_
 
+#ifndef NULL
+#define NULL ((void *)0)
+#endif
+
 #include "Either.h"
 #include "Maybe.h"