Parslet: SystemStackError: stack level too deep

Question

I am working on a new programming language rip, and I'm having trouble getting to the bottom of some infinite loops. Is there a way to print out each rule as it gets called, such that I can see the rules that are recursing? I've tried walking through the code in my head, and I just don't see it. Any help would be much appreciated.

Answer 1

To flesh out Raving Genius’s answer:

The method to patch is actually Parslet::Atoms::Context#lookup. View it on GitHub (permalink to current version). In your own code, you can patch that method to print obj like this:

class Parslet::Atoms::Context
  def lookup(obj, pos)
    p obj
    @cache[pos][obj.object_id]
  end
end

Run that code any time before you call parse on your parser, and it will take effect. Sample output:

>> parser = ConsistentNewlineTextParser.new
=> LINES
>> parser.parse("abc")
LINES
(line_content:LINE_CONTENT NEWLINE){0, } line_content:LINE_CONTENT
(line_content:LINE_CONTENT NEWLINE){0, }
line_content:LINE_CONTENT NEWLINE
LINE_CONTENT
WORD
\\w{0, }
\\w
\\w
\\w
\\w
NEWLINE
dynamic { ... }
FIRST_NEWLINE
'? '
'
'?
'
'
'
LINE_CONTENT
=> {:line_content=>"abc"@0}

Answer 2

I figured it out: editing Parslet::Atom::Context#lookup to output the obj parameter will show each rule as it is being called.

Answer 3

My branch of Parslet automatically detects endless loops, and exits out reporting expression that is repeating without consuming anything.

https://github.com/nigelthorne/parslet

see Parse markdown indented code block for an example.