UndefVarError from macro

General Usage
1

How can I fix this error?

using MacroTools: postwalk

macro mymac(e)
    postwalk(x -> (x isa Expr && x.head isa Symbol && x.head == :. 
    ? esc(:($x isa String ? (return $x) :  $x isa Int ? $(x).val : throw("invalid"))) : x), e)
end

@mymac function foo(v)
    y = identity(v).ATTR
    return y + 1
end
foo(3) # ERROR: LoadError: UndefVarError: v not defined
2 
@macroexpand(@mymac function foo(v)
    y = identity(v).ATTR
    return y + 1
end)

shows

:(function Main.foo(var"#133#v")
      #= C:\Users\Win10\source\repos\julia\idioms\test\problem53.jl:8 =#
      #= C:\Users\Win10\source\repos\julia\idioms\test\problem53.jl:9 =#
      var"#132#y" = if (identity(v)).ATTR isa String
              return (identity(v)).ATTR
          else
              if (identity(v)).ATTR isa Int
                  (identity(v)).ATTR.val
              else
                  throw("invalid")
              end
          end
      #= C:\Users\Win10\source\repos\julia\idioms\test\problem53.jl:10 =#
      return var"#132#y" + 1
  end)

It looks to me like you have to adapt the escaping in your macro?