anchor.diff:                      Column = None
                   }
           }
  +
       member this.Unary(source : SourceInfo, unary : UnaryExpr) =
           let operand = this.Expr(unary.Operand)
           {   Expr.Source = source
  
positive.code:                     Column = None
                  }
          }
      member this.FunctionInvocation(source : SourceInfo, func : FunctionInvocationExpr) =
          match scope.Model.Builtin.Functions.TryFind(func.FunctionName) with
          | None -> failAt source <| sprintf "No such function: ``%O``" func.FunctionName
  
negative.code:                         Column = None
                      }
              }
  
      member this.Similarity(source : SourceInfo, sim : SimilarityExpr) =
          let input = this.Expr(sim.Input)
          let pattern = this.Expr(sim.Pattern)
  