diff --git a/src/test.nim b/src/test.nim
index 04d1ec1..7b59e01 100644
--- a/src/test.nim
+++ b/src/test.nim
@@ -11,10 +11,6 @@ import print
 {.experimental: "caseStmtMacros".}
 
 type
-  ParsePosition = tuple
-    column, line, currentLine: int
-    atNewLine: bool
-
   ParseError = tuple
     unexpected: string
     expected: seq[string]
@@ -31,9 +27,13 @@ type
   Parser* = ref object
     state: ParserState
     tokens: seq[Token]
-
   ParserResult* = Result[Parser, (Parser, string)]
 
+  # Builder[T]* = ref object
+  #   parser: ParserResult,
+  #   tree: seq[T],
+  # BuilderResult* = Result[Builder, (Builder, string)]
+
 func getOrElse*[T, E](self: Result[T, E], otherwise: T): T =
   if self.isOk():
     self.v
@@ -114,6 +114,26 @@ func str(s: string): (Parser -> ParserResult) {.inline.} =
       p = p.flatMap(ch(c))
     return p
 
+# proc foldTokens[T](
+#   parserResult: ParserResult,
+#   builderResult: BuilderResult[T],
+#   fn: Parser -> T,
+# ): BuilderResult[T] =
+#   builderResult.flatMap((b: Builder) => Builder(
+#     parser: parserResult,
+#     tree: parserResul
+#   ))
+
+proc foldTokens[T](
+  parserResult: ParserResult,
+  onError: T,
+  onSuccess: seq[Token] -> T,
+): T =
+  if parserResult.isOk():
+    onSuccess(parserResult.unsafeGet().tokens)
+  else:
+    onError
+    # onError(parserResult.error)
 
 when isMainModule:
   let fooParser = initParser("FOO_BAR")
@@ -124,5 +144,9 @@ when isMainModule:
     ch('A'),
     ch('R'),
   ])
+  .foldTokens(
+    "Error",
+    xs => xs.foldl(a & b.value, "")
+  )
 
   echo fooParser