Foo: imports Sort from m

Foo(_) : scopes Sort

yields

amb(
  [ [ BindingRule(
        Var("Foo")
      , []
      , [ ImportClause(
            [ WildcardImport(
                [Restricted([], NamespaceRef("Sort"))]
              , []
              , RefScope(VarRef("m"))
              , Current()
              , []
              )
            ]
          )
        ]
      )
    , BindingRule(
        NoAnnoList(Op("Foo", [Wld()]))
      , []
      , [ScopeClause([NamespaceRef("Sort")])]
      )
    ]
  , [ BindingRule(
        Var("Foo")
      , []
      , [ ImportClause(
            [ WildcardImport(
                [Restricted([], NamespaceRef("Sort"))]
              , []
              , Context(All(), NamespaceRef("m"), VarRef("Foo"), [], Current())
              , Current()
              , []
              )
            ]
          )
        ]
      )
    , BindingRule(
        NoAnnoList(Tuple([Wld()]))
      , []
      , [ScopeClause([NamespaceRef("Sort")])]
      )
    ]
  ]
)

Submitted by Sebastian Erdweg on 8 May 2014 at 11:05

The second alternative parses it as

 Foo: imports Sort from m Foo

 (_): scopes Sort

This is a typical ambiguity for terms with optional parentheses for nullary constructors and tuples.

Possible fixes:

1. Make parentheses mandatory.
2. Introduce a keyword in the imports ... from t clause, e.g. imports ... from term t.
3. Introduce an end-of-rule marker.

I’m also encountering this issue. The following NaBL snippet gives me an ambiguity error:

binding rules

	Entity(name, super, _):
		imports Property from super
		
	EntityNoSuper(name, _):
		defines Entity name

The AST is ambiguous between this:

[BindingRule(Op("Entity",
 [Var("name"),Var("super"),Wld]),NoWhere,
 [ImportClause([WildcardImport([Restricted([],NamespaceRef(CurrentLanguage,"Property"))],
 [],Context(All,NamespaceRef(CurrentLanguage,"super"),VarRef("EntityNoSuper"),
 [],Current),Current,NoWhere)])]),BindingRule(Tuple([Var("name"),Wld]),NoWhere,
 [DefClause(Explicit,Unique,NamespaceRef(CurrentLanguage,"Entity"),VarRef("name"),
 [],Current,NoWhere)])]

And this:

[BindingRule(Op("Entity",[Var("name"),Var("super"),Wld]),NoWhere,
 [ImportClause([WildcardImport([Restricted([],NamespaceRef(CurrentLanguage,"Property"))],
 [],RefScope(VarRef("super")),Current,NoWhere)])]),BindingRule(Op("EntityNoSuper",
 [Var("name"),Wld]),NoWhere,
 [DefClause(Explicit,Unique,NamespaceRef(CurrentLanguage,"Entity"),VarRef("name"),
 [],Current,NoWhere)])]

---

A possible solution is to require into. In this case into current scope can already be used.

binding rules

	Entity(name, super, _):
		imports Property from super into current scope
		
	EntityNoSuper(name, _):
		defines Entity name

For now, you can circumvent this by introducing another binding rules phrase after the import rule.