bugfix: stack traces; first class iterators almost working

tests/run/titer8.nim

@@ -0,0 +1,33 @@
+discard """
+  output: '''tada
+ta da'''
+"""
+# Test first class iterator:
+
+import strutils
+
+iterator tokenize2(s: string, seps: set[char] = Whitespace): tuple[
+  token: string, isSep: bool] {.closure.} =
+  var i = 0
+  while i < s.len:
+    var j = i
+    if s[j] in seps:
+      while j < s.len and s[j] in seps: inc(j)
+      if j > i:
+        yield (substr(s, i, j-1), true)
+    else:
+      while j < s.len and s[j] notin seps: inc(j)
+      if j > i:
+        yield (substr(s, i, j-1), false)
+    i = j
+
+for word, isSep in tokenize2("ta da", whiteSpace):
+  if not isSep:
+    stdout.write(word)
+echo ""
+
+proc inProc() =
+  for word, isSep in tokenize2("ta da", whiteSpace):
+    stdout.write(word)
+
+inProc()