Turning a tuple to json

[archnim]

Hello world. Here is my code:
    
    
    import std/[json]
    
    var
      t = (a: "A", b: 5)
    
    echo pretty %t
    
    
    Run

Here is what the compiler says:
    
    
    t.nim(6, 13) Error: type mismatch: got <tuple[a: string, b: int]>
    
    
    Run

Please, how can create my json node ?