Replace frustration.rs with literate-programmed version that matches the README. Use idiomatic Rust constructors.

README.md

@@ -199,6 +199,18 @@ out with print!().
         self.tos = (self.tos.wrapping_sub(1)) & (N - 1);
         return val;
     }
+```
+
+Finally, here is a function that creates a new stack.
+Because these are circular stacks it doesn't matter where top-of-stack
+(tos) starts off pointing.  I arbitrarily set it to the highest index so
+the first value pushed will wind up at index 0, again because this
+makes the stack look nicer when printed out.
+
+```rust
+    fn new() -> Stack<N> {
+        return Stack {tos: N-1, mem: [0; N]};
+    }
 }
 ```
 ### Designing a stack CPU
@@ -243,25 +255,21 @@ struct Core {
 }
 ```
 
-Now for a helper to initialize the CPU.
+Finally, let's write a function that creates and returns a CPU for us to use.
 
 ```rust
-fn new_core() -> Core {
-    let c = Core {
-        ram: [0; ADDRESS_SPACE],
-        ip: 0,
-        dstack: Stack {tos: 15, mem: [0; 16]},
-        rstack: Stack {tos: 31, mem: [0; 32]}};
+use std::convert::TryInto;
 
-    return c;
-}
+impl Core {
+    fn new() -> Core {
+        return Core {
+            ram: [0; ADDRESS_SPACE],
+            ip: 0,
+            dstack: Stack::new(),
+            rstack: Stack::new()}
+    }
 ```
 
-Because these are circular stacks it doesn't matter where top-of-stack
-(tos) starts off pointing.  I arbitrarily set it to the highest index so
-the first value pushed will wind up at index 0, again because this
-makes the stack look nicer when printed out.
-
 ## 1.1 - The instruction set
 
 Now we have a CPU sitting there but it does nothing.
@@ -290,13 +298,9 @@ So now we will make the CPU do those things.
 We'll start off by teaching it how to access memory, and then we will
 define the instruction set.
 
-```rust
-impl Core {
-```
-
 ### Memory access
 
-Start with a helper to read a number from the specified memory address.
+Now let's write a function to read a number from the specified memory address.
 
 ```rust
     fn load(&self, addr: u16) -> u16 {
@@ -2642,7 +2646,7 @@ Finally, start the machine.
 ```rust
 fn main() {
     /* Create the machine */
-    let mut c = new_core();
+    let mut c = Core::new();
 
     /* Put the dictionary into memory */
     build_dictionary(&mut c);