Type-safe finite state machines in zig！

sdzx-1 · November 21, 2024, 3:44pm

I used to develop type-safe finite state machines in haskell.https://github.com/sdzx-1/typed-fsm

The same effect can be achieved by relying on some programming conventions in zig.

I made some examples using typed-fsm-zig: GitHub - sdzx-1/typed-fsm-zig: typed-fsm-zig

typed-fsm + gui is a very good choice!!!

sdzx-1/typed-fsm-zig/blob/610f5eed5c305e313eea62579a11ef2bf016597b/examples/atm-gui.zig#L169


      
                          const st = std.fmt.bufPrintZ(&tmpBuf, "amount: {d}", .{ist.amount}) catch "error";
                          rl.drawText(st, 100, 90, 30, rl.Color.green);
                          if (ist.resource.disponse.toButton()) return .{ .Disponse = .{ .v = 10 } };
                          if (ist.resource.changePin.toButton()) return .ChangePin;
                          if (ist.resource.eject.toButton()) return .EjectCard;
                      }
                  }
              };
          }
          
          pub fn changePinMsg(end: AtmSt) type {
              return union(enum) {
                  PushNum: struct { v: u8, wit: W(end, .changePin) = .{} },
                  Update: W(end, .ready),
          
                  pub fn genMsg(ist: *const InternalState) @This() {
                      while (true) {
          
                          // render
                          rl.beginDrawing();
                          defer rl.endDrawing();

sdzx-1 · November 21, 2024, 3:47pm

The advantages described here also exist in zig!

sdzx-1 · January 1, 2025, 3:46am

Added more introduction！

sdzx-1 · May 8, 2025, 6:16am

The latest typed-fsm-zig simplifies the state and allows state transition functions based on state transition messages, which is a victory for abstraction.

code

Perken · May 11, 2025, 5:54pm

Hello,

is there a way to have the GUI loop managed externally from the state machine logic?

From what I understand, your FSM can’t retain static typing unless genMsg runs the gui loop to retrieve the user input.
But, there are situations where the GUI can’t be run directly from genMsg(), for example if it’s managed by a host application.
I’ve looked into it, and I can’t find a solution: no matter what, if genMsg doesn’t own the loop, then you have to resort to using a dispatcher function, which nullifies the strong typing…

Any hints?

harryprayiv · May 11, 2025, 6:03pm

This is really cool. Thanks for sharing.

I wonder if you’ve seen the CREM module?

IMO, it has some pretty interesting ideas that go a long way toward making illegal states materialize as type errors. It uses Singletons to do much of that. I wonder is that plausible or possible in Zig?

Another cool feature is being able to generate a diagram of all possible states and transitions solely using the code.