Alternative implementation of tovalues

tests/modules/streaming.jq

@@ -1,41 +1,49 @@
 
 # Filter and adjust streamed values so that only values from the .th
 # level are output.
-def trunc(inputs):
-  . as $n | inputs | . as $input | if (.[0]|length) > 1 then setpath([0];$input[0][1:]) else empty end;
+def trunc(stream):
+  . as $n | stream | . as $input | if (.[0]|length) > $n then setpath([0];$input[0][$n:]) else empty end;
 
 # Reduce streamed values back to normal
 def tovalues(i):
+  def debug(msg): . as $dot | [msg, .] | debug | $dot;
   foreach i as $item (
-    # [<current value being built>,
-    #  <is current value valid?>,
-    #  <previous, complete value>,
-    #  <is previous value valid?>]
-    [null,false,null,false];
+    [null,false,null];
 
     # Updator
     # 
     # If the new $item is a top-level value,
     # then clear out the current value
-    if ($item[0]|length) == 0 then [null,false,.[2],.[3]]
-    # else if the new $item terminates the current value,
-    # then rotate the current value into the previous value slot.
-    elif ($item|length) == 1 and ($item[0]|length) < 2 then [null,false,.[0],.[1]]
-    else . end |
-    . as $state |
+    .                   as [$cur, $cur_isvalid, $prev]  |
+    $item               as [$path, $leaf]               |
+    ($item|length > 1)  as $has_leaf                    |
+    ($item|length == 1) as $closing                     |
+    ($path|length)      as $plen                        |
+    # if the new $item terminates the current value, then cur is ready
+    # for extraction and we'll start building a new value with the next
+    # inputs
+    if ($plen == 0) or # top-level scalar
+       ($closing and $plen < 2) then [null,false,$cur]
+    # else continue building up cur
+    else . end                                          |
+    . as [$cur, $cur_isvalid, $prev]                    |
     # If the new $item has a leaf, upate the current value
-    if ($item|length) > 1 and ($item[0]|length) > 0 then
-      [.[0]|setpath(($item|.[0]); ($item|.[1])),    # update current value
+    if $has_leaf and $plen > 0 then
+      [$cur|setpath(($path); $leaf),              # update current value
       true,                                         # current value is now valid (if, perhaps, incomplete)
-      $state[2],                                    # previous value is unchanged
-      $state[3]]                                    # previous value is unchanged
+      $prev]                                        # previous value is unchanged
     else .
     end;
 
     # Extractor
     #
+    . as [$cur, $cur_isvalid, $prev]                    |
+    $item as [$path, $leaf]                             |
+    ($item|length > 1) as $has_leaf                     |
+    ($item|length == 1) as $closing                     |
+    ($path|length) as $plen                             |
     # If previous value is valid, output it
-    if ($item[0]|length) == 1 and ($item|length == 1) and .[3] then .[2] else empty end,
+    if $plen == 1 and $closing then $prev else empty end,
     # and/or if the new $item is a top-level scalar, output it
-    if ($item[0]|length) == 0 then $item[1] else empty end
+    if $plen == 0 then $leaf else empty end
     );