Exactly. It’s an incredibly helpful debugging tool in ruby, and I would love to see something like this on the elixir side!
mike_bianco
mudasobwa
Creator of Cure
Offtopic: This quote made my day, thank you so much! I am to use it to point out any architecture/design/performance/database/younameit issue from now on. Like in CR, when there is, say, an if on function argument instead of different pattern matching function clauses:
Is there supposed to be an
a?
And even in the real life, talking to my wife; it is applicable literally everywhere.
1
hauleth
It should present value of a form the place where exception was thrown. AFAIK it is not possible at all in Erlang, but this is how better-errors does it - it allows you to check values of local variables in place where exception was raised.
0
OvermindDL1
Ah, not sure I’ve ever used a language like that outside of stackless python. In C++/OCaml/Rust/Etc… once the stack frame is unwound anything that was existing before is now gone (although with some unsafe pointing munging you can sometimes get some old values, but don’t rely on that at all).
I’m not even sure how that is safe to do without heap-based frames. I’m guessing Ruby uses heap-based frames. The BEAM’s actors use stack-based frames so it is not safe to do such a mapping.
Except on the BEAM by the time the exception is unwound that stack frame is already gone and potentially even GC’d.
Except that stack frame is gone. If you want bindings from the thrown site then they need to be packaged up into the exception itself, which binding() would be great to use for, maybe make a library that has a dthrow/draise for a decorated throw and raise along with a dtry for a decorated exception handler for them? 
What’s better-errors? Link please? I’m quite curious. ^.^
0
michallepicki
It’s possible in Java (at least in IntelliJ IDE), C++ (both VS debugger and gdb), C# and Python, so I’m pretty sure you used a language like that.
0
OvermindDL1
Those debuggers specifically overwrite the exception thrower with their own code (python adds a trace handler to the call, python’s debugging is actually very similar to the beam’s but at a far more fine-grained level) so as to be able to debug at the point of throwing instead of in the handler. Once you have unwound to the handler though, the information is gone.
0
michallepicki
OvermindDL1
Not necessarily, rather a library to decorate the throw/raise/try calls with extra information, though you’d have to remember to use it in each file when necessary.
0
hauleth
That is why I am saying that such library cannot exist in Elixir world, as there is just not enough data 
It is library for Rails that provide better error pages on Rails exceptions in development.
And it still would provide less informations as it would not handle errors in dependencies. Also you cannot overwrite try in Elixir at all (it is special form).
0
OvermindDL1
Ah, never used Rails or Ruby, only better_errors library I’d heard of was for OCaml. ^.^;
Well you could but you’d have to apply a preprocessor to the files before feeding them into the compiler, doable but would require a mix.exs line added and a lot of work in the library.
But a macro that processes the entire module can modify it.
0