add docs to state

src/lib.rs

@@ -0,0 +1 @@
+pub mod state;

src/state.rs

@@ -1,28 +1,136 @@
-// State monad
+/** State Monad
+
+Represents a computation using `State` to produce a value of type `Value` and a new state.
+
+Computations can be combined using [bind](WithState::bind) or [zip](WithState::zip).
+*/
 pub struct WithState<'c, Value, State>(Box<dyn FnOnce(State) -> (Value, State) + 'c>);
 
 impl <'c, Value, State> WithState<'c, Value, State> {
+    /**
+    Constructs a new state monad out of the contained computation.
+
+    The input computation takes the previous state, and returns a
+    tuple containing the computed value and the new state.
+
+    ```
+    use statemonad::state::WithState;
+
+    // wrap a computation that returns the initial_state + 1, and changes the state to its double.
+    let s : WithState<i32, i32> = WithState::of(|init_state| (init_state + 1, init_state * 2));
+
+    // run the state monad with initial state 2
+    let (val,state) = s.run(2);
+
+    assert_eq!(val, 3);
+    assert_eq!(state, 4);
+    ```
+    */
     pub fn of(f: impl FnOnce(State) -> (Value, State) + 'c) -> WithState<'c, Value, State> {
 	WithState(Box::new(f))
     }
     
+    /**
+    Runs the state monad, running all contained computations in order
+    and returns the final computed value and state.
+
+    ```
+    use statemonad::state::WithState;
+
+    // create a state monad that computes the value as the initial state * 2, and doesn't modify the state.
+    let s : WithState<f32, i32> = WithState::of(|init_state| (init_state as f32 * 2.0, init_state));
+
+    // run the state monad with an initial state 1, getting the final value and final state.
+    let (val, state) = s.run(1);
+
+    assert_eq!(val, 2.0);
+    assert_eq!(state, 1);
+
+    ```
+    */
     pub fn run(self, s: State) -> (Value, State) {
 	self.0(s)
     }
 
+    /**
+    Binds two state computations together.
+
+    Expects a function from the previously computed value, to a new state monad.
+    
+    # Examples
+
+    ```
+    use statemonad::state::WithState;
+
+    // initialize the value to the initial state, add 1 to the state
+    let s : WithState<i32, i32> = WithState::of(|oldstate| (oldstate, oldstate + 1)) 
+	// Set the value to the old state, multiply the state by 2
+	.bind(|oldvalue| WithState::of(|oldstate| (oldstate, oldstate * 2))) 
+	// "do-nothing", return the old value and keep the state the same, closure has to be `move` due to referencing the outside value.
+	.bind(|oldvalue| WithState::of(move |oldstate| (oldvalue, oldstate))); 
+
+
+    let (computed_val,final_state) : (i32,i32) = s.run(0);
+
+    assert_eq!(computed_val, 1); // value was initially 0, then set to state when state was 1
+    assert_eq!(final_state, 2); // state was originally 0, then added 1, then multiplied by 2
+    ```
+    */
     pub fn bind<'cn, NewValue>(self, f: impl FnOnce(Value) -> WithState<'cn, NewValue, State> + 'cn) -> WithState<'cn, NewValue, State>
     where 'c: 'cn, State : 'cn, Value : 'cn {
-	WithState::<'cn, NewValue, State>::of(move |n| {
-	    let (x,sp) = self.run(n);
-	    f(x).run(sp)
+	WithState::<'cn, NewValue, State>::of(move |old_value| {
+	    let (new_value,new_state) = self.run(old_value);
+	    f(new_value).run(new_state)
 	})
     }
 
+    /**
+    Combine two state monad computations together.
+    Creates a new state monad with the result value being a tuple containing both input state monads.
+    The `State` type must be the same for both state monads. 
+
+    # Examples
+
+    ```
+    use statemonad::state::WithState;
+    
+    // initialize one state monad computing a string value, and one computing a float.
+    let s : WithState<String, i32> = WithState::of(|oldstate| (String::from(""), oldstate + 1));
+    let s2 : WithState<f32, i32> = WithState::of(|oldstate| (1.0, oldstate));
+
+    // zip them together
+    let s3 : WithState<(String,f32), i32> = s.zip(s2);
+
+    // compute both values together!
+    let ((val1,val2),state) = s3.run(0);
+
+    assert_eq!(val1, "");
+    assert_eq!(val2, 1.0);
+    
+    ```
+    */
     pub fn zip<'cn, NewValue>(self, st: WithState<'cn, NewValue, State>) -> WithState<'cn, (Value,NewValue), State>
     where 'c: 'cn, State: 'cn, Value: 'cn, NewValue: 'cn {
 	self.bind(|aa| st.map(|bb| (aa,bb)))
     }
 
+    /**
+    Modify the computed value without changing the state.
+
+    # Examples 
+    ```
+    use statemonad::state::WithState;
+
+    let s : WithState<f32, i32> = WithState::of(|oldstate| (1.0, oldstate));
+
+    let s2 = s.map(|oldval| oldval * 2.0);
+
+    let (val, state) = s2.run(0);
+
+    assert_eq!(val, 2.0);
+    assert_eq!(state, 0);
+    ```
+    */
     pub fn map<'cn, NewValue>(self, f: impl FnOnce(Value) -> NewValue + 'cn) -> WithState<'cn, NewValue, State>
     where 'c: 'cn, State : 'cn, Value : 'cn {
 	WithState::<'cn, NewValue, State>::of(move |n| {