Combining Programs and State Machines

Basic instruction set

A basic instruction sets that supports interactions with state machines is FMN (Focus Method Notation).

Instructions

f.a(x)

Here, f is the focus of the instruction, and a(x) its co-instruction part (or co-action). The bracket pair can be empty. A focus is loaded the first time it is used.
It returns the value replied by the co-instruction.

f.p:a(x)

Here, p is the prefix of the action that will be performed, indicating a particular copy of the state machine. A copy of the state machines is created the first time the prefix is used.
It returns the value replied by the co-instruction.

Alternative versions of the above instructions:

f.a:x

f:i.a:x

Here, i is the instance of the method.

Available state machines

• Console
  Co-actions: println(s) in which s is a string of characters.
  The action println prints its argument.
• smbr - boolean register
  Co-actions: set(true), set(false), eq(true), eq(false)
  The co-actions set(true) and set(false) reply true. The co-actions eq(true) and eq(false) reply false until the register is set, after which eq(b) replies true whenever b is the current value of the register, and false otherwise.
• smnnr - natural number register
  Co-actions: set(i), eq(i) in which i is a natural number
  The replies of the co-actions are simular to that of smbr.
• smnnc - natural number counter
  Co-actions: succ(), pred(), isZero()
  The counter always starts with value zero, and the action pred() leaves the counter at zero if it is zero.
• smnns - natural number stack
  Co-action: push(i), pop(), topEq(i) in which i is a natural number.
  The stack always starts empty, and the action pop() leaves the empty stack empty.

Examples

• Consider the following PGLEc program.

  smbr.x:set(true);
  smbr.y:set(false);
  + smbr.x:eq(true) {;
      Console.println(x is true);
  }{;
      Console.println(x is false);
  };
  + smbr.y:eq(true) {;
      Console.println(y is true);
  }{;
      Console.println(y is false);
  }
  

  Upon execution the result will be:

  x is true
  y is false
  

• Fibonacci numbers