Python's with statement implemented in Nimrod

with.nim

import macros

macro with_closing*(opening, holder: expr, body: stmt): stmt {.immediate.} =
  var code = newNimNode(nnkStmtList)
  var def = newNimNode(nnkVarSection)
  # Create the variable assignment, holder + opening
  var idents = newIdentDefs(holder, newEmptyNode())
  idents[2] = opening
  def.add(idents)
  code.add(def)

  # Create the try block and insert the body statements.
  var tr = newNimNode(nnkTryStmt)
  tr.add(body)

  # Now create a finally block which invokes close() on the holder.
  var fin = newNimNode(nnkFinally)
  fin.add(newStmtList(newCall(newIdentNode("close"), holder)))
  tr.add(fin)
  code.add(tr)
  result = newBlockStmt(code)

with_closing(Open("test.txt", fmWrite), f):
  f.write("Hey there\n")
  f.write("This looks nice!")

echo "Hey"