Super-reference split

[mantkiew]

Decouple super and reference. This allows providing both in a clafer declaration:

cmd : Port -> Command

Also, inheritance from primitive types is not allowed anymore. Previously : integer was rewritten to -> integer; however, since now a reference can be provided independently, we cannot perform that rewrite. For example, rewriting x : integer -> string would either require ability to have two references or choosing one. Perhaps the rewrite could still be provided in cases when no reference is given but that would encourage keeping using the bad style. UPDATE: after the pull request, desugaring of : into -> for primitive types was added back and it is performed when safe (that is, there's no reference).

Major grammar changes:

Clafer. Clafer ::= Abstract GCard PosIdent Super Reference Card Init Elements ;

SuperEmpty. Super ::= ;
SuperSome. Super ::= ":" SetExp ;

ReferenceEmpty. Reference ::= ;
ReferenceSet. Reference ::= "->" SetExp ;
ReferenceBag. Reference ::= "->>" SetExp ;

InitConstant. InitHow ::= "=" ;
InitDefault. InitHow ::= ":=" ;

IR changes:

data IClafer 
...
 , _parentUID :: UID 
 , _super :: Maybe PExp
 , _reference :: Maybe IReference
...

data IReference
 = IReference
 { _isSet :: Bool
  , _ref :: PExp
  }

The ISuper datatype has been removed.

Consequences

The uniqueness constraint for set reference clafers is no longer created in desugarer. Instead, the Alloy and Choco generators produce the required output for bags and sets.

The default super clafer is no longer produced by desugarer. It is represented in IR by _super=Nothing. It is also missing from the desugared clafer output for simplicity des.cfr and the XML output.

Stats are computed differently, because super and ref are counted independently.

We can now implement redefinition.