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3707 :: Dynamic import of packages at macro-time

• r3d9u11 (orginal) [2018-03-30T13:59:07+02:00] view original

  Hi. Does Nim supports anything like a "dynamic loading of packages"? For example something like a program:

  import pack0
  
  init(1)
  echo someProc(5) #must display 6
  
  init(2)
  echo someProc("qwe") #must display qwerty
  Run

  and 3 packages with some logic. pack0.nim ("proxy" package) contains:

  var dstBack = 0 # some variable-indetifier (will indicate, from wich package someProc will be called)
  macro init*(back:int) = # some initialization macros, who sets variable's value before "someProc" was called
    dstBack = back
  
  macro someProc* = # some macros, who will return "someProc" from destination package (in choice of "dstBack")
    case: dstBack
    of 1:
      #check that pack1 is available...
      #if true:
      return pack1.someProc
      #else show compiler's exception with an due message
    of 2:
      #check that pack1 is available...
      #if true:
      return pack2.someProc
      #else show compiler's exception with an due message
    else:
      discard
    return proc () = discard #return empty function
  Run

  nim due package must be accessed only when dstBack contains certain value (1 or 2). pack1.nim:

  proc someProc*(a:int): int =
    result a += 1
  Run

  pack2.nim:

  proc someProc*(a:string): string =
    result a & "rty"
  Run

  Is it possible to realize this scheme in Nim? Thanks.

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• r3d9u11 (orginal) [2018-03-30T16:16:46+02:00] view original

  well, I'm found similar theme. This works:

  import macros
  
  macro load*(modulesSeq: varargs[untyped]): untyped =
    result = newStmtList()
    for module in modulesSeq:
      result.add parseStmt("from " & $module & " import nil")
  
  const a = 0
  
  when a == 0:
    load strutils
    echo strutils.join(@[1,2,3], ", ")
  elif a == 2:
    load asdsadasd # will excepted if set a to 2
  Run

  cool

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