diff --git a/private/lex.nim b/private/lex.nim
new file mode 100644
index 0000000..f385f1b
--- /dev/null
+++ b/private/lex.nim
@@ -0,0 +1,429 @@
+#            NimYAML - YAML implementation in Nim
+#        (c) Copyright 2015 Felix Krause
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+
+import lexbase, streams, strutils
+
+type
+  StringSource* = object
+    src: string
+    pos: int
+    line, lineStart: int
+
+  SourceProvider* = concept c
+    advance(c) is char
+    lexCR(c)
+    lexLF(c)
+
+  YamlLexer*[T: SourceProvider] = ref object
+    source: T
+    inFlow: bool
+    literalEndIndent: int
+    nextImpl, stored: proc(lex: YamlLexer[T], t: var LexerToken): bool
+    c: char
+    buf*: string not nil
+    indentation*: int
+
+  LexerToken* = enum
+    ltYamlDirective, ltYamlVersion, ltTagDirective, ltTagShorthand,
+    ltTagUrl, ltUnknownDirective, ltUnknownDirectiveParams,
+    ltDirectivesEnd, ltDocumentEnd, ltStreamEnd, ltIndentation, ltQuotedScalar,
+    ltScalarPart, ltEmptyLine, ltSeqItemInd, ltMapKeyInd, ltMapValInd,
+    ltBraceOpen, ltBraceClose, ltBracketOpen, ltBracketClose, ltComma,
+    ltLiteralTag, ltTagSuffix, ltAnchor, ltAlias
+
+  YamlLexerError* = object of Exception
+
+# templates
+
+template advance(lex: YamlLexer[BaseLexer], step: int = 1) =
+  lex.source.bufpos.inc(step)
+  lex.c = lex.source.buf[lex.source.bufpos]
+
+template advance(lex: YamlLexer[StringSource], step: int = 1) =
+  lex.source.pos.inc(step)
+  lex.c = lex.source.src[lex.source.pos]
+
+# lexer states
+
+proc outsideDoc[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc yamlVersion[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc tagShorthand[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc tagUri[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc unknownDirParams[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc expectLineEnd[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc blockStyle[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc blockStyleInline[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc plainScalarPart[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc flowStyle[T](lex: YamlLexer[T], t: var LexerToken): bool
+proc streamEnd[T](lex: YamlLexer[T], t: var LexerToken): bool
+
+# interface
+
+proc newYamlLexer*(source: Stream): YamlLexer[BaseLexer] = 
+  result = YamlLexer[T](source: BaseLexer(), inFlow: false, buf: "",
+      nextImpl: outsideDoc[T])
+  result.source.open(source)
+  result.c = result.source.buf[result.source.bufpos]
+
+proc newYamlLexer*[T: StringSource](source: string, startAt: int = 0):
+    YamlLexer[T] =
+  result = YamlLexer[T](nextImpl: outsideDoc, buf: "", source:
+      StringSource(src: source, pos: startAt, lineStart: startAt, line: 1),
+      inFlow: false, c: source[startAt])
+
+proc next*(lex: YamlLexer): LexerToken =
+  while not lex.nextImpl(result): discard
+
+# implementation
+
+const
+  space          = {' ', '\t'}
+  lineEnd        = {'\l', '\c', EndOfFile}
+  spaceOrLineEnd = {' ', '\t', '\l', '\c', EndOfFile}
+  digits         = {'0'..'9'}
+  flowIndicators = {'[', ']', '{', '}', ','}
+
+template debug(message: string) {.dirty.} =
+  when defined(yamlDebug):
+    try: styledWriteLine(stdout, fgBlue, message)
+    except IOError: discard
+
+proc generateError(lex: YamlLexer, message: string):
+    ref YamlLexerError {.raises: [].} =
+  result = newException(YamlLexerError, message)
+  result.line = lex.lineNumber
+  result.column = lex.bufpos + 1
+  result.lineContent = lex.getCurrentLine(false) &
+      repeat(' ', lex.getColNumber(lex.bufpos)) & "^\n"
+
+template handleCR(lex: YamlLexer[BaseLexer]) =
+  lex.source.bufpos = lex.source.handleCR(lex.source.bufpos)
+
+template handleCR(lex: YamlLexer[StringSource]) =
+  lex.source.pos.inc()
+  if lex.source.src[lex.source.pos] == '\l': lex.source.pos.inc()
+  lex.source.lineStart = lex.source.pos
+  lex.source.row.line.inc()
+
+template handleLF(lex: YamlLexer[BaseLexer]) =
+  lex.source.bufpos = lex.source.handleLF(lex.source.bufpos)
+
+template handleLF(lex: YamlLexer[StringSource]) =
+  lex.source.pos.inc()
+  lex.source.lineStart = lex.source.pos
+  lex.source.row.line.inc()
+
+proc directiveName(lex: YamlLexer) =
+  while lex.c notin spaceOrLineEnd:
+    lex.buf.add(lex.c)
+    lex.advance()
+
+proc yamlVersion[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  debug("lex: yamlVersion")
+  while lex.c in space: lex.anvance()
+  if lex.c notin digits: raise lex.generateError("Invalid YAML version number")
+  lex.buf.add(lex.c)
+  lex.advance()
+  while lex.c in digits:
+    lex.buf.add(lex.c)
+    lex.advance()
+  if lex.c != '.': raise lex.generateError("Invalid YAML version number")
+  lex.buf.add('.')
+  lex.advance()
+  if lex.c notin digits: raise lex.generateError("Invalid YAML version number")
+  lex.buf.add(lex.c)
+  lex.advance()
+  while lex.c in digits:
+    lex.buf.add(lex.c)
+    lex.advance()
+  if lex.c notin spaceOrLineEnd:
+    raise lex.generateError("Invalid YAML version number")
+  t = ltYamlVersion
+  result = true
+  lex.stored = outsideDoc[T]
+  lex.nextImpl = expectLineEnd[T]
+
+template nextIsPlainSafe(lex: YamlLexer[BaseLexer], inFlow: bool): bool =
+  case lex.source.buf[lex.source.bufpos + 1]
+  of spaceOrLineEnd: result = false
+  of flowIndicators: result = not inFlow
+  else: result = true
+
+template nextIsPlainSafe(lex: YamlLexer[StringSource], inFlow: bool): bool =
+  case lex.source.src[lex.source.pos + 1]
+  of spaceOrLineEnd: result = false
+  of flowIndicators: result = not inFlow
+  else: result = true
+
+proc tagShorthand[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  debug("lex: tagShorthand")
+  while lex.c in space: lex.advance()
+  if lex.c != '!': raise lex.generateError("Tag shorthand must start with a '!'")
+  lex.buf.add(lex.c)
+  lex.advance()
+
+  if lex.c in spaceOrLineEnd: discard
+  else:
+    while lex.c != '!':
+      case lex.c
+      of 'a' .. 'z', 'A' .. 'Z', '0' .. '9', '-':
+        lex.buf.add(lex.c)
+        lex.advance()
+      else: raise lex.generateError("Illegal character in tag shorthand")
+    lex.buf.add(lex.c)
+    lex.advance()
+  if lex.c notin spaceOrLineEnd:
+    raise lex.generateError("Missing space after tag shorthand")
+  lex.nextImpl = tagUri[T]
+
+proc tagUri[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  debug("lex: tagUri")
+  while lex.c in space: lex.advance()
+  if lex.c == '!':
+    lex.buf.add(lex.c)
+    lex.avance()
+  while true:
+    case lex.c
+    of  spaceOrLineEnd: break
+    of 'a' .. 'z', 'A' .. 'Z', '0' .. '9', '#', ';', '/', '?', ':', '@', '&',
+       '-', '=', '+', '$', ',', '_', '.', '~', '*', '\'', '(', ')':
+      lex.buf.add(lex.c)
+      lex.advance()
+    else: raise lex.generateError("Invalid character in tag uri: " &
+        escape("" & lex.c))
+
+proc unknownDirParams[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  var c = lex.curChar()
+  while c notin lineEnd + {'#'}:
+    lex.advance()
+    c = lex.curChar()
+  t = ltUnknownDirectiveParams
+  result = true
+  lex.stored = outsideDoc[T]
+  lex.nextImpl = expectLineEnd[T]
+
+proc expectLineEnd[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  debug("lex: expectLineEnd")
+  result = false
+  while lex.c in space: lex.anvance()
+  while true:
+    case lex.c
+    of '#':
+      lex.advance()
+      while lex.c notin lineEnd: lex.advance()
+    of EndOfFile:
+      lex.nextImpl = streamEnd[T]
+      break
+    of '\l':
+      lex.handleLF()
+      lex.nextImpl = lex.stored
+      break
+    of '\c':
+      lex.handleCR()
+      lex.nextImpl = lex.stored
+      break
+    else:
+      raise lex.generateError("Unexpected character (expected line end): " &
+          escape("" & lex.c))
+
+proc possibleDirectivesEnd[T](lex: YamlLexer[T], t: var LexerToken) =
+  lex.advance()
+  if lex.c == '-':
+    lex.advance()
+    if lex.c == '-':
+      lex.advance()
+      if lex.c in spaceOrLineEnd:
+        t = ltDirectivesEnd
+        lex.nextImpl = blockStyleInline[T]
+        return
+      lex.buf.add('-')
+    lex.buf.add('-')
+  elif lex.c in spaceOrLineEnd:
+    lex.advance()
+    t = ltSeqItemInd
+    lex.nextImpl = blockStyleInline[T]
+    return
+  lex.buf.add('-')
+  lex.nextImpl = plainScalarPart[T]
+  lex.indentation = 0
+  t = ltIndentation
+
+proc possibleDocumentEnd[T](lex: YamlLexer[T], t: var LexerToken) =
+  lex.advance()
+  if lex.c == '.':
+    lex.advance()
+    if lex.c == '.':
+      lex.advance()
+      if lex.c in spaceOrLineEnd:
+        t = ltDocumentEnd
+        lex.nextImpl = expectLineEnd[T]
+        lex.stored = outsideDoc[T]
+        return
+      lex.buf.add('.')
+    lex.buf.add('.')
+  lex.buf.add('.')
+  lex.nextImpl = plainScalarPart[T]
+  lex.indentation = 0
+  t = ltIndentation
+
+proc outsideDoc[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  case lex.c
+  of '%':
+    lex.advance()
+    lex.directiveName()
+    case lex.buf
+    of "YAML": lex.nextImpl = yamlVersion[T]
+    of "TAG": lex.nextImpl = tagShorthand[T]
+    else: lex.nextImpl = unknownDirParams[T]
+    break
+  of '-':
+    lex.possibleDirectivesEnd(t)
+    return true
+  of '.':
+    lex.possibleDocumentEnd(t)
+    return true
+  of spaceOrLineEnd + {'#'}:
+    lex.indentation = 0
+    while lex.c == ' ':
+      lex.indentation.inc()
+      lex.advance()
+    if lex.c in spaceOrLineEnd + {'#'}:
+      lex.nextImpl = expectLineEnd[T]
+      lex.stored = outsideDoc[T]
+      return false
+  else: lex.indentation = 0
+  lex.nextImpl = blockStyleInline[T]
+  t = ltIndentation
+  result = true
+
+proc blockStyle[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  case lex.c
+  of '-':
+    lex.possibleDirectivesEnd(t)
+    return true
+  of '.':
+    lex.possibleDocumentEnd(t)
+    return true
+  of spaceOrLineEnd + {'#'}:
+    lex.indentation = 0
+    while lex.c == ' ':
+      lex.indentation.inc()
+      lex.advance()
+    if lex.c in spaceOrLineEnd + {'#'}:
+      lex.nextImpl = expectLineEnd[T]
+      lex.stored = blockStyle[T]
+      t = ltEmptyLine
+      return true
+  else: lex.indentation = 0
+  lex.nextImpl = blockStyleInline[T]
+  t = ltIndentation
+  result = true
+
+proc possibleIndicatorChar[T](lex: YamlLexer[T], indicator: LexerToken,
+    t: var LexerToken): bool =
+  if lex.nextIsPlainSafe(false):
+    lex.nextImpl = plainScalarPart[T]
+    lex.stored = blockStyleInline[T]
+    result = false
+  else:
+    t = indicator
+    result = true
+    lex.advance()
+    while lex.c in space: lex.advance()
+    if lex.c in lineEnd:
+      lex.nextImpl = expectLineEnd[T]
+      lex.stored = blockStyle[T]
+
+proc flowIndicator[T](lex: YamlLexer[T], indicator: LexerToken,
+    t: var LexerToken, inFlow: static[bool]): bool {.inline.} =
+  t = indicator
+  lex.advance()
+  while lex.c in space: lex.advance()
+  if lex.c in lineEnd:
+    lex.nextImpl = expectLineEnd[T]
+    when inFlow: lex.stored = flowStyle[T]
+    else: lex.stored = blockStyle[T]
+
+proc blockStyleInline[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  case lex.c
+  of ':': result = lex.possibleIndicatorChar(ltMapValInd, t)
+  of '?': result = lex.possibleIndicatorChar(ltMapKeyInd, t)
+  of '-': result = lex.possibleIndicatorChar(ltSeqItemInd, t)
+  of lineEnd + {'#'}:
+    result = false
+    lex.nextImpl = expectLineEnd[T]
+    lex.stored = blockStyle[T]
+  of '\"':
+    lex.doubleQuotedScalar()
+    t = ltQuotedScalar
+    result = true
+  of '\'':
+    lex.singleQuotedScalar()
+    t = ltQuotedScalar
+    result = true
+  of '>', '|':
+    # TODO
+    result = true
+  of '{': result = lex.flowIndicator(ltBraceOpen, t)
+  of '}': result = lex.flowIndicator(ltBraceClose, t)
+  of '[': result = lex.flowIndicator(ltBracketOpen, t)
+  of ']': result = lex.flowIndicator(ltBracketClose, t)
+  else:
+    lex.nextImpl = plainScalarPart[T]
+    lex.stored = blockStyleInline[T]
+    result = false
+
+proc plainScalarPart[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  debug("lex: plainScalar")
+  block outer:
+    while true:
+      lex.buf.add(lex.c)
+      lex.advance()
+      case lex.c
+      of space:
+        let lenBeforeSpace = lex.buf.len()
+        while true:
+          lex.buf.add(lex.c)
+          lex.advance()
+          case lex.ch
+          of lineEnd + {'#'}:
+            lex.buf.setLen(lenBeforeSpace)
+            lex.nextImpl = expectLineEnd[T]
+            lex.stored = if lex.inFlow: flowStyle[T] else: blockStyle[T]
+            break outer
+          of ':':
+            if lex.nextIsPlainSafe(): break
+            else:
+              lex.buf.setLen(lenBeforeSpace)
+              lex.nextImpl = lex.stored
+              break outer
+          of flowIndicators:
+            if lex.inFlow:
+              lex.buf.setLen(lenBeforeSpace)
+              lex.nextImpl = lex.stored
+              break outer
+            else:
+              lex.buf.add(lex.c)
+              lex.advance()
+              break
+          of space: discard
+          else: break
+      of flowIndicators:
+        if lex.inFlow:
+          lex.nextImpl = lex.stored
+          break
+      of ':':
+        if not lex.nextIsPlainSafe(): break outer
+      else: discard
+  t = ltScalarPart
+  result = true
+
+proc flowStyle[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  result = false
+
+proc streamEnd[T](lex: YamlLexer[T], t: var LexerToken): bool =
+  t = ltStreamEnd
+  result = true
\ No newline at end of file
diff --git a/private/streams.nim b/private/stream.nim
similarity index 100%
rename from private/streams.nim
rename to private/stream.nim
diff --git a/test/tlex.nim b/test/tlex.nim
new file mode 100644
index 0000000..8a95a3d
--- /dev/null
+++ b/test/tlex.nim
@@ -0,0 +1,18 @@
+import ../private/lex
+
+import unittest
+
+type
+  TokenWithValue = object
+    case kind: LexerToken
+    of ltScalarPart, ltQuotedScalar:
+      value: string
+    else: discard
+
+proc assertEquals(input: string, expected: varargs[TokenWithValue]) =
+  let lex = newYamlLexer[StringSource](input)
+  
+
+suite "Lexer":
+  test "Empty document":
+    
\ No newline at end of file
diff --git a/yaml.nim b/yaml.nim
index 8aa457c..b215d33 100644
--- a/yaml.nim
+++ b/yaml.nim
@@ -750,7 +750,7 @@ setTagUri(float64, "!nim:system:float64", yTagNimFloat64)
 include private.tagLibrary
 include private.events
 include private.json
-include private.streams
+include private.stream
 include private.presenter
 include private.parse
 include private.hints