Case statement won't compile

[Mike Jones]

I had some code that worked, then after a change won't compile, but I don't understand why.

The code that compiled and worked had three value constructors and a FSS that switched states between two states, AtomicA and Atomic B. You can see this i the code here:

  datatype pstate =

    | AtomicA of ()

    | AtomicB of ()

    | Hang of ()

  typedef state = @{ addr= uint8, ps= pstate }

  fun process (ch:int, s: &state) : void = let

    val sn  = case s.ps of

              | AtomicA () =>  let

                                val _ = case cast{char}(ch) of

                                        | 'z' => let

                                          val _ = do_something()

                                          in s.addr := s.addr; s.ps := AtomicA end 

                                        | _ => let _ in _ end  

                                in _ end

              | AtomicB () =>  let _

                                val _ = case cast{char}(ch) of

                                        | 'z' => let

                                          val _ = do_something()

                                          in s.addr := s.addr; s.ps := AtomicB end  

                                        | _ => let _ in _ end  

                                in _ end

              | Hang () => _

  in

    _

  end

Then I added two constructors, and made the transitions more complex, as the case for AtomicA can change to one of two states. Then it won't compile and gives the error:

undefined reference to `atsruntime_handle_unmatchedval'

The range of lines is the entire top self case statement.

I change the top level case from "case" to "case+" and it compiles.

Can anyone explain why this makes it compile?

Note that all cases are covered because they all have a "_" pattern at the bottom to match on.

  datatype pstate =

    | AtomicA of ()

    | NonAtomicA of ()

    | AtomicB of ()

    | NonAtomicB of ()

    | Hang of ()

  typedef state = @{ addr= uint8, ps= pstate }

  fun process (ch:int, s: &state) : void = let

    val sn  = case s.ps of

              | AtomicA () =>  let

                                val _ = case cast{char}(ch) of

                                        | 'z' => let

                                          val _ = do_something()

                                          in s.addr := s.addr; s.ps := NonAtomicA end 

                                        | 'T' => let

                                          val mode = serial_poll()

                                          val ns = if mode = 1 then AtomicA else AtomicB

                                          in s.addr := s.addr; s.ps := ns end

                                        | _ => let _ in _ end  

                                in _ end

              | AtomicB () =>  let _

                                val _ = case cast{char}(ch) of

                                        | 'z' => let

                                          val _ = do_something()

                                          in s.addr := s.addr; s.ps := NonAtomicB end  

                                        | 'T' => let

                                          val mode = serial_poll()

                                          val ns = if mode = 1 then AtomicA else AtomicB

                                          in s.addr := s.addr; s.ps := ns end  

                                        | _ => let _ in _ end  

                                in _ end

              | NonAtomicA () => let

                                in _ end

              | NonAtomicB () => let _

                                in _ end

              | Hang () => _

  in

    _

  end

[Hongwei Xi]

In ATS, pls use either case+ or case-; if you use case, the compiler currently always add a run-time catchall.

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