anchor.diff:      ast.CallExpression expression,
       hir.IdentifierExpression target,
     ) {
  +    assert(target != null);
       assert(target.identifier is hir.PropertyIdentifier);
       final identifier = target.identifier as hir.PropertyIdentifier;
   
  
positive.code:       hir.Expression.functionCall(
          getId(expression),
          target,
          hirArgumentMap,
        ),
      ]);
    }
  
negative.code:         }
        }
  
        // Constructor call.
        if (target is hir.IdentifierExpression &&
            target.identifier is hir.ReflectionIdentifier) {
          final identifier = target.identifier as hir.ReflectionIdentifier;
          // TODO: Ensure this is a constructor call.
          // if (identifier.id.isConstructor) {
          return lowerConstructorCall(expression, target);
          // }
        }
  
        throw CompilerError.unsupportedFeature(
          'Callable expressions are not yet supported (target $target).',
          location: ErrorLocation(resourceId, expression.span),
        );
      });
  