[ANN] heap-console - Haskell

I was working on this tool for inspecting values at runtime recently - https://hackage.haskell.org/package/heap-console
Basically, it let's you pause at presence of special combinators, starting console which you can use to inspect and force custom bindings.
If anyone wants some more powerful alternative to traceShow, you can give it a go - personally I'm excited to try it out in compiler-ish stuff where I often want to explore big, nested values to find out what went wrong. :smile:

cool!

Bindings can be automatically created with functions like inspectD what does Bindings mean here?

They're just values bound to some names inside of console
Will make it more clear in docs, thanks for mentioning!

so if I use inspectD 42 what binding is automatically created? it might be a good idea to show this in the example for inspectD

Yeah, it gets bound to it as mentioned in inspects description

I guess I will move longer descriptions to D versions and add queries for it in examples, thanks!

ah I guess what was confusing me is that I expected the inspectD version to be the one creating bindings, as opposed to inspect, because this is the first time inspectD is mentioned in the docs and it's in the context of bindings

something that would be really cool is a pattern synonym that you can add to a particular case match and get all the bindings from that case match in the "console" automatically

but I'm not sure this is possible without a source plugin or something

D is for Data - they otherwise behave in the same way

Georgi Lyubenov // googleson78 said:

something that would be really cool is a pattern synonym that you can add to a particular case match and get all the bindings from that case match in the "console" automatically

That's a cool idea - maybe I could make quasiquoter like

[i| ... |]

that works in both expressions and patterns

well I kind of realised my original suggestion is easily doable as is, no? the issue is more that you need a way to access the "fields" of the constructor if it's not a record type

e.g. indexing?

e.g.

pattern InspectD :: Data a => a -> a
pattern InspectD x <- (inspectD -> x)

and now you can write

data Person = Person {name :: String}
x :: Person
case x of
  InspectD (Person ...) -> ...

and

it.name

right?

Yeah - I thought you mean binding variables introduced by pattern

though I wonder whether it's big win over (inspectD -> Person ...) :smile:

yeah I guess the only thing missing is reusing the actual names you've bound in the program

Yeah, that's hard without TH or plugin

very interesting!

This is super cool. Looking forward to trying it out in a project!

Thank you guys for feedback! One question - do you think it would be better to preserve all bound values between console runs? (not just those bound with evidence-like combinators)

I would say no, as it could get expensive in some apps. Having the ability to optionally do that might be cool, but I'd default to no.

Hmm, thing is, this basically only changes behaviour of it and binds created in console
I guess binding lots of things with evidence is more probable, and in that case, I could implement the opposite - cleaning of binds when closing console

But if that's going to be an option, I probably need to start thinking about persistent configuration - how would that work in app that may be tested through cabal run or from completely different location?

I have no idea what black magic you use for evidence, but couldn't you use that to have a function that turns a flag on or off?

it's an IORefcontaining a Map!

a noinline global IORef*

so to answer @Vladimir Ciobanu 's question: yes!

Oh, lol. An actual global variable. Neato. So why not stick the option in there, and provide on/off helpers.

I'm not that worried about adding bindings based on control flow - but I feel more uneasy about doing so with configuration :sweat_smile:

Not like this is meant for something other than debugging, but still

Version on GitLab now preserves state across console runs - and I've added option to clean bindings on console exit (now it can be at least slightly useful)

BTW, what do you think about searching for .heap-console conf file in location of executable?

And :save command that dumps settings there

are there any other settings?

(also, I'd recommend in the location of the executable, and also recursively in parents, so it's easier to use with something like stack)

Georgi Lyubenov // googleson78 said:

(also, I'd recommend in the location of the executable, and also recursively in parents, so it's easier to use with something like stack)

Sounds reasonable - will try it

prompt = "heap-console> "
hehe, nice

this "global" heap-console config seems to have turned out pretty nice for usage

put a universal one in home and forget about it

Next up on list are Generic support and refactoring of console - and I should really start writing tests :sweat_smile:

I've pushed new version on GitLab with refactored console that should be easier to extend and should make it easier to support auto-complete - once I finish Generic I'll make a new release and start working on tests

@Georgi Lyubenov // googleson78 I've just realized why Generic may be slightly more problematic - it hides actual laziness of input value, so lazy indexing isn't very informative

I guess I'll mention it as a drawback, similarly to problems with non-Data combinators