Debugger

[thinkerbot]

Signatures

No problem to determine incorrect node signatures at the call, process, and process_block levels. The output should notify the node, and ideally the join causing the problem. Once a trace is in place, the join could be found by searching back in the trace for the specified inputs:

trace.reverse_each
  if node.joins has the present task
  and the inputs come from the join (match object, or find object in an array)
  then consider the join found (or search everything... maybe the issue is upstream?)

And once you have the join, help can be provided to suggest what needs to be done to fix the error.

Replay

A breakpoint could be added to step through the workflow. In this case, or perhaps generally, the trace should be saved to disk allowing quick replay. Will not work with objects that cannot be serialized, and that's ok. Simply encourages people not to pass around IO or blocks, or to fix YAML.