typesafeprintf.nim

import macros, strutils

type
  TokenKind = enum
    FInt, FString, Text

  Token = object
    case kind: TokenKind
    of FInt, FString: nil
    of Text: c: String

iterator tokenize(format: string): Token =
  var i = 0
  while True:
    case format[i]
    of '%':
      case format[i+1]
      of 'd': yield Token(kind: FInt)
      of 's': yield Token(kind: FString)
      of '\0': break
      else: error("Incorrect format string.")
      i.inc
    of '\0': break
    else:
      yield Token(kind: Text, c: $format[i])
    i.inc

macro printf(format: Static[String], params: Varargs[Expr]): Stmt =
  echo(treeRepr(params))
  var i = 0
  var stringLit = ""
  for tok in tokenize(format):
    case tok.kind
    of FInt:
      if i >= params.len: error("Too many arguments in format string.")
      if params[i].kind != nnkIntLit: error("Expected Int got " & $params[i].kind)
      stringLit.add($params[i].intVal)
      i.inc
    of FString:
      if i >= params.len: error("Too many arguments in format string.")
      if params[i].kind != nnkStrLit: error("Expected String got " & $params[i].kind)
      stringLit.add(params[i].strVal)
      i.inc
    of Text: stringLit.add tok.c
  if i < params.len: error("Too many arguments to printf.")
  result = quote do:
    echo(`stringLit`)

printf("test %d %s", 10, 10)