Typed finite state machine!

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#1

Hi everyone, I have developed a new library typed-fsm.
It allows writing typed finite state machines.
It has many advantages:

  1. Focus on the right message

  2. Top-to-bottom design for easy refactoring

  3. Conducive to building complex state machine systems

    • Type guarantees will not produce incorrect function calls when written
    • With the help of the type system, we can define many state processing functions and then call each other recursively with confidence.

  4. There is a sanity check. If you miss some items for pattern matching, the compiler will issue a warning, and there will also be a warning for invalid items.

Detailed explanation here.
Do you have any suggestions?

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#2

Nice library! In case you’d had a look at it already , would you mind explaining how it compares to motor: Type-safe effectful state machines in Haskell?

#3

I don’t fully understand motor.

But I feel that the motor uses the Bob Atkey Indexed Monad.

typed-fsm uses Conor McBride Indexed Monad.

I feel that for fsm, McBride Indexed Monad is the more correct choice.

More detailed instructions here

Indexed Monad

1 Like
#4

Complete ATM example.
Tracks the number of checkPin attempts on the type, statically guaranteeing no more than three attempts.|

atm
atm1377×1027 62 KB

confidence-in-types

start ATM
-> current ATMSt: Ready
ins card
-> current ATMSt: CardInserted Z
checkPin 1
-> current ATMSt: CardInserted (S Z)
checkPin 2
-> current ATMSt: CardInserted (S (S Z))
checkPin 3
-> test 3 times, eject card!
-> current ATMSt: Ready
ins card
-> current ATMSt: CardInserted Z
checkPin 1234
-> current ATMSt: Session
getAmount
-> User Amount: 1000
-> current ATMSt: Session
dispense 100
-> Use dispense 100
-> Now User Amount: 900
-> current ATMSt: Session
dispense 100
-> Use dispense 100
-> Now User Amount: 800
-> current ATMSt: Session
eject
-> current ATMSt: Ready
1 Like