Tack.Credo.Check.CorePurity (pica v0.1.0)

Basics

This check has a base priority of high and works with any version of Elixir.

Explanation

The pure core takes values as arguments: no clock read, no config read, no process, no IO.

CLAUDE.md, Approach & architecture: the pure domain rules are a boundary declaration with type: :strict, so a core module reaching a context, a read model or any external library fails the build. This check is the part of the core's contract the compiler cannot hold. What Boundary cannot see is the standard library: DateTime.utc_now/0, Application.get_env/3, spawn/1 and File.read/1 are :elixir/:kernel, and a core module calling one compiles in silence.

Four categories, each with the shape that replaces it:

• Clock reads — take the instant as an argument. A small Clock module at the boundary reads the wall clock and hands the value to a pure core fold.
• Config reads — take the value as an argument. Where a question genuinely needs both config and a pure fold, it gets its own small module above the core.
• Unseeded randomness — every source of randomness derives from an injected integer seed, through the state-passing :rand API (:rand.seed_s/2 with :rand.uniform_s/1) or :erlang.phash2/1,2. The process-dictionary API (:rand.uniform/0, Enum.random/1) is not reproducible, and every run must replay.
• Processes and IO — the core is values in, values out.

Scope this check to the core in .credo.exs with a files: filter; it says nothing about the rest of the tree, where all four categories are ordinary.

Check-Specific Parameters

There are no specific parameters for this check.

General Parameters

Like with all checks, general params can be applied.

Parameters can be configured via the .credo.exs config file.