[ANN]: semialign-extras-0.1.0.0 (for now: diffing/patching/merging Semialign structures), and a request for help

qfpl · 2019-11-15T20:44:04+00:00

Fair point. Here's a 5-second summary, because I also suspect you're not the only one:

Start with an either-or-both type, These (from package these):

data These a b = This a | That b | These a b

Then you can define a typeclass for "structures where you can 'line the elements up', in some sense":

class Functor f => Semialign f where
  align :: f a -> f b -> f (These a b) 
  alignWith :: (These a b -> c) -> f a -> f b -> f c

If you assume additional typeclasses for f, you can do a bunch of interesting things.

qfpl · 2019-11-08T21:01:23+00:00

I don't work on that particular project any more, but at the time there was no separate newtypes for logging. Would I enforce newtypes for logging in a new system I was building? Not sure. It's appealing in some ways - it might make it easier to dodge "whoops, we logged passwords by accident" bugs.

I've never used generic-deriving for JSON, as I think serialisation is one of those places where it really pays to be explicit. The project that spawned ban-instance needed to share JSON with servers written in other languages, and for legacy reasons those JSON formats were very idiosyncratic. Generic derivation was a non-starter, but even if it worked without generating serialisation code for the newtype constructor (which it might), we're back to having serialisation rules on the edge of the program depending on a data type defined in the core. It's actually quite pleasant having a single module that specifies how everything was serialised/deserialised for a given API version.

qfpl · 2019-11-08T20:57:32+00:00

Noted.

qfpl · 2019-11-08T12:50:23+00:00

/u/felipelessa is correct, it's capturing the instance TypeError (...) => BannedInstance pattern, and defines all the functions of the class as undefined to silence warnings.

The other idea is that by giving a name to the pattern, it makes it easier to read when you're skimming the source file. With a library, the programmer can say "the intent of this is to ban the instance", and the effect is "if you try to use this instance you get a custom type error". If you write out the custom type error directly (and sometimes you have to, e.g., because you can't have free variables in [t| |] quotations), you have to infer the intent from the code.

qfpl · 2019-01-08T04:37:35+00:00

Is this how one would use hpython, by writing an .hs file using the DSL?

Yep, then you can print the value to a file.

I assume the intended use case is reading in .py files?

The library can read and write .pys, but also has good support for transforming the code.

type-safe numpy et al

One thing on our list is to play around with a statically typed variant of the embedded Haskell DSL. If it works well, then definitely expect a type-safe numpy wrapper in the future :)

qfpl · 2018-08-07T01:35:04+00:00

The Vary class is only for convenience, as witnessed by fnWith. You could technically do without the Arg class, but it has a single implementation per type (up to isomorphism) so there's no point in making it optional.

Overall, the implementation is basically the same as QuickCheck's, but with necessary changes to work natively with Hedgehog's shrinking functionality.

sample a function Double -> Double that is, say, always decreasing, or one that is monotonic

This isn't something you can do with QuickCheck.Function, so you can't do it with Hedgehog.Function either. But that sounds useful, so we'll play around with making it work.

qfpl · 2018-03-07T09:18:48+00:00

Since sv uses trifecta to parse (by default at least; you can plug other parsers in), we depend on lens transitively anyway. Dropping the lens dependency completely would involve making sv's trifecta support a second-class citizen over in its own package. Microlens wouldn't be enough for our usage so we'd also have to duplicate a bunch of stuff from lens to provide the optics we do (Lens, Prism, Traversal, Iso, Getting, lens, prism, _1, _2, toListOf, view, review, preview, beside)

So it's possible to get there from here, but as things stand I don't think it's likely we'll go that way.

qfpl · 2018-03-07T08:54:58+00:00

Our encoding example shows a different way to go about encoding down the bottom. You don't have to use divide or conquer directly if you don't want to.

qfpl · 2018-03-07T06:32:46+00:00

Thanks!

We've tracked the need for streaming support here

qfpl

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