More compact & nicer toString for states; added ! for step functions; bugfix for tape length

The new toString takes only one line and is a better reproduction of
the notation from Sudkamp, Languages and Machines, 1997.

The IterableClass functions now have ! on input types that are
iterated, so that these arguments are computed for sure.

There was a bug (!! index too large or the like) for some machines
that 'walked off the tape' on the right side. The tape is now auto-
matically extended with Nothing (blank) cells. When the machine
walks off the tape on the *left*, the machine still terminates
abnormally.

1 files changed, 5 insertions, 1 deletions

diff --git a/TuringMachines.icl b/TuringMachines.icl
index b37233c..f13ca7d 100644
--- a/TuringMachines.icl
+++ b/TuringMachines.icl
@@ -30,7 +30,10 @@ where
 instance toString (TuringMachineState a) | toString a
 where
     toString st=:{state,tapeHead,tape,running}
-    = toString running +++ " turing machine in state " +++ toString state +++ ", tape head at " +++ toString tapeHead +++ ".\nTape: " +++ toString tape
+    = toString (take tapeHead tape) +++
+        "[q" +++ toString state +++ "]" +++
+        toString (drop tapeHead tape) +++
+        " (" +++ toString running +++ ")"
 
 instance == Direction
 where
@@ -55,6 +58,7 @@ instance step (TuringMachineState a) | == a
 where
     step st=:{machine,state,tapeHead,tape,running}
         | running <> Running    = st
+        # tape                  = if (length tape < tapeHead + 1) (tape ++ [Nothing]) tape
         # move                  = machine.transition state (tape!!tapeHead)
         | move == Halt          = {st & running = Normal}
         # (Step state write dir) = move