Decode this bug

[Stephen Weeks]

> should 
> val x = Id.newString "foo"
> val y = Id.newString "foo"
> 
> Id.equals(x,y) --> true ?
> 
> val x = Id.fromString "foo"
> val y = Id.fromString "foo"
> 
> Id.equals(x,y) --> true ?

No.  Both of these should return false.  Newly created identifiers
always have a ref cell in them that uniquely identifies them
(actually, it is the property list for the identifier).  The different 
constructors (fromString, new, newString, newNoname) all build new
identifiers that are unequal to any other -- the only difference is in 
the print name of the variable.

> Does MLton expect each variable to be defined exactly once? (i.e. to I need
> to alpha convert my program before hand..)

Yes.  Every label, variable, etc. must be defined in exactly one
place.  This is so that the property lists can be used.

> inferHandlers ==> 
> ==> 
> Bug: fold2
> 
> uncaught exception Bug

This is the handler inference pass.  The type system must be able to
assign a unique local handler stack to each local jump.