myzip.nim

macro myzip(x: ForLoopStmt): untyped =
  x.expectKind nnkForStmt
  result = newStmtList()
  echo x.treeRepr
  echo "\n##################"

  # Count the number of idents:
  var ident_count = 1
  while x[ident_count + 1].kind == nnkIdent:
    inc ident_count

  assert ident_count == 1 # no tuple deconstruction yet ...

  # Check the smallest seq:
  x[ident_count].expectKind nnkCall

  let last_container = x[ident_count].len

  var len = high(int)
  for i in 1 ..< last_container:
    len = min(len, x[ident_count][i].len)

  # Create a new for loop iteration container
  var c = nnkBracket.newTree()
  for j in 0 ..< len: # iterate over the containers
    var p = nnkPar.newTree()
    for i in 1 ..< last_container: # iterate over the index
      p.add x[ident_count][i][j]
    c.add p

  # Add the iteration variable
  var newFor = newTree(nnkForStmt)
  for i in 0 ..< ident_count:
    newFor.add x[i]

  # Add the new containers
  newFor.add c

  # Add the body
  newFor.add x[^1]

  # Finalize
  result.add newFor


for a in myZip([1, 2, 3, 11, 14], [4, 5, 6, 11, 12, 15], [7, 8, 9, 13, 16]):
  echo a

# Promising with a few caveats
# Questions:
#   - this doesn't work with variables like "x" instead of [1, 2, 3, 11, 14]
#   - this works only if the containers have all the same type, as I'm mixing the arrays