[MLton-user] signal handling an mllex based filter

[Michael Norrish]

I have a filter that reads from stdin and writes to stdout.  The input 
is lexed with an mllex program that recognises the tokens and outputs 
the necessary transformations.

In other words, the end of the program looks like

  val lexer = filter.makeLexer (read_from_stream instream) state
  val _ = lexer()

I want the user to be able to hit control-c to reset the state of the 
lexer.  In particular, if the lexer can get into different internal 
states if it's in the middle of recognising a quotation literal 
(something with delimiters).

It has MLlex code like

   <START>{quote-begin} (YYBEGIN INQUOTE; continue());
   ...

   <INQUOTE>{quote-end} (YYBEGIN START; continue());
   <INQUOTE>...

In Moscow ML, I did some magic to get SIGINT recognised as an Interrupt 
exception, and did

   lexer() handle Interrupt => lexer()

In Poly/ML, I had to do a little different magic, but was again able to 
get SIGINT recognised as an Interrupt exception.  I thus had the same 
code again.

In MLton, I'm confused.

I can handle SIGINT with MLton.Signal.setHandler, but it seems as if I 
am going to have to explicitly set myself up with a master thread that 
repeatedly creates slave threads to run lexer().  Then in the handler, I 
can just switch to the master, leaving the interrupted slave to expire 
through lack of attention.

Is this stylistically and pragmatically correct?

Thanks,
Michael