Statement macro applied on proc

[tzumao]

Hi,

I am still very new to nim, so what I am trying to do may not be making sense 
at all. The thing I am trying to do with nim macro is simple: create a 
duplication of a proc. Everything remains the same except the name is changed 
to [proc_name]_duplicate (I plan to do some manipulation with the proc but I 
stucked here) The code is: 
    
    
    import macros
    
    macro duplicate(procStmt: typed): typed =
      procStmt.expectKind nnkStmtList
      let procDef = procStmt[0]
      procDef.expectKind nnkProcDef
      
      let name = newIdentNode($procDef[0] & "_duplicate")
      
      var params: seq[NimNode]
      params = @[]
      for param_id in 0..<len(procDef[3]):
        params.add copy(procDef[3][param_id])
      
      let body = copy(procDef[6])
      
      return newStmtList(newProc(name, params, body))
    
    duplicate:
      proc foo(x: int): void =
        echo(x)
    

and when compiling I get: 
    
    
    duplicate.nim(19, 1) template/generic instantiation from here
    duplicate.nim(21, 10) Error: internal error: environment misses: x
    

if the proc has a return value like this: 
    
    
    duplicate:
      proc foo(x: int): int =
        result = x
    

then there is a different error: 
    
    
    duplicate.nim(19, 1) template/generic instantiation from here
    duplicate.nim(21, 5) Error: illegal capture 'result'
    

Am I doing something wrong? What is the correct way to do this?

Thanks!