Pyc → Structs on Steroids



Blog post, announcing Pyc package. It allows transparent validation across inserted data with Exvalibur, chaining functions in a monadic-like way, and exposes all the keys as local variables inside methods declared with defmethod (without compilation warnings.)

It also reasonably implements Access behaviour for wrapped structs and Collectable protocol with validation.


If the struct has more than three fields,
pattern matching in the function head is to be copy-pasted over the whole module or extracted into a cryptic macro.

Yeah, I tend to use the shorter_maps library for that but even it can still get very long and the formatter breaks things up very weird at times… >.>

Even then, although, it quickly becomes hardly maintainable due to unused variables warnings thrown whenever one calls the all-in-one macro and does not use all the variables injected.

You can just do quote generated: true do to silence most warnings (though not variable unused I think?), or in that case can transform the body to add hoisted versions. Even then that won’t work if you need to pass in 2 of that struct in the same head. :slight_smile:

I needed a monadic behaviour there (once any call in the pipe failed, I want the rest transformations to be skipped and the error immediately returned back.)

You really should look at all of expede’s packages on I use a few of them pretty excessively… >.>

guards: %{check_bar: "is_map(bar)"}}]

And reason this is a string instead of just:

guards: %{check_bar: is_map(bar)}}]

Since the use can be a macro anyway, so it can read it straight? :slight_smile:

Looks like an interesting library overall though. :slight_smile:


Hey @mudasobwa. It’s always great to see people take on problems.

There’s a few thing about these libraries that would make them more likely to be used by others. The first big one for Exvalibur is making the source code more readily available. The hexdocs don’t link to any source code, and I couldn’t find it with some cursory googling either. I had to create a project, add it as a dep, and then open the deps directory to get a look at it.

The code contains a LOT of Code. function calls. This is almost always a sign that things aren’t quite right. A lot of it is to support the strings which, as @OvermindDL1 notes, is completely unnecessary because of Elixir’s built in macro support.


I doubt I understand. Hexdocs have a built-in support for links to the source and docs are indeed linked to the code.

Also, I would be grateful to see how to use macros to avoid strings there.


Ah, that’s my mistake, the page looked like the top module doc and I looked for </> and didn’t see it. I see the code now, I wonder why it wasn’t higher on google.

As far as the macros go, it’s a pretty large topic. I’d consider the guides, and the Metaprogramming Elixir book. I’m a little short on time at the moment but I may be able to comment later with more details. The short version is that your Code.string_to_quoted is what the compiler already does. Try using just is_map(val) and see what the input to your function is.

The functions inside Code should basically never be called at runtime. They’re not optimized for it and can lead to a variety of issues.


This is how Exvalibur works now :slight_smile:

I do not remember why exactly I went with binaries, but I am pretty sure it was because I wanted things TBD and I failed to do it properly.


Sure. The users of this package put guards in their config.exs files though.


Recalled. To be used in config.exs. Also, I should support plain guards, thanks.