Projects and examples

Small pieces of code to accompany the posts. Each download is plain text; the linked note explains the assumptions and expected behavior.

The five Python test examples require Python 3.10 or newer and only the standard library. Run a downloaded file with python3 filename.py; a successful run ends with OK. C examples use C11; the checked-add example is a function to place in a test harness. Haskell and schema snippets are illustrative.

Go users: the historical zenhack.net/go/util import path points to its original upstream repository. The package page explains version compatibility.

• Promise pipelining removes a wait, not a dependency

  Illustrative protocol or diagnostic sketch. promise-pipelining.txt

• A useful setup log starts with the question it can answer

  Illustrative protocol or diagnostic sketch. debugging-records.txt

• A command line is an argument vector before it is a shell string

  Locally checked Python example. subprocess-argument-boundary.py

• Endianness belongs in the format, not in a lucky host assumption

  Locally checked Python example. endianness-is-a-format-choice.py

• A virtual environment has an interpreter boundary

  Locally checked Python example. venv-interpreter-boundary.py

• Make an invalid state unrepresentable at the interface

  Illustrative Haskell definition. types-as-interface-decisions.hs

• Validate CSV headers before building dictionaries

  Python 3.10+ · standard library · executable unittest checks. how-can-you-validate-a-csv-header-quickly.py

• Testing a schedule cache across feed revisions

  Python 3.10+ · standard library · executable unittest checks. how-can-you-test-a-cache-after-a-feed-version-changes.py

• A durable idempotency key in one SQLite transaction

  Python 3.10+ · standard library · executable unittest checks. what-does-idempotency-mean-in-a-network-protocol.py

• Parsing GTFS times beyond midnight

  Python 3.10+ · standard library · executable unittest checks. why-can-gtfs-times-exceed-24-00-00.py

• CSV round trips: commas, quotes and embedded newlines

  Python 3.10+ · standard library · executable unittest checks. how-should-a-csv-file-handle-commas-in-text.py

• A byte stream does not know where your messages end

  Locally checked Python example. transport-is-not-framing.py

• Why len(x) is not just x.__len__() in disguise

  Locally checked Python example. python-special-method-lookup.py

• A Python name is a binding, not a box containing a copy

  Locally checked Python example. python-bindings-and-mutation.py

• Changing a Cap’n Proto schema without renumbering history

  Illustrative schema. capnp-schema-evolution.capnp

• A closure in C is a function plus an environment

  Locally checked C example. closures-without-nested-functions.c

• C is an abstract machine, even on familiar hardware

  Locally checked C example. c-abstract-machine.c

Upstream projects

These are independent projects discussed in the notes, maintained by their respective developers.

Sandstorm

A platform for self-hosted web applications, with sharing and isolation built around grains.

Cap’n Proto

A schema language, serialization format and capability-oriented RPC protocol.

Haskell Cap’n Proto

The upstream project’s GitHub mirror. Its README points to its official home on Codeberg.

Tempest

An upstream systems project; the repository reading note explains what its source can tell us.