When I was building SwiftBash I made surprisingly quick headway on the basic CLI utilities — jq, awk, sed, grep. Each one is a small, well-scoped language, and once you sit down with the spec it really is just a parser and an evaluator.

Then I hit a wall. The two CLIs I reach for most as a working developer aren’t tiny languages — they’re gh and glab, the GitHub and GitLab clients. And right next to them, the granddaddy of all dev CLIs: git. These aren’t 2,000-line tools. gh alone is roughly fifty thousand lines of Go, with subcommand trees, OAuth flows, REST + GraphQL clients, pagination, archive extraction, jq filtering — the works. Reimplementing all of that by hand felt like a year of evenings.

But the source code is right there on GitHub. And I have a coding agent. So I began to wonder: shouldn’t Opus 4.7 1M (extra-high) be able to translate cli/cli into Swift for me, given the original as ground truth?

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A few days ago I introduced SwiftBash — a sandboxed bash interpreter written in pure Swift. At the end of the four-green-checkmarks post I promised the next instalment would be about something else: SwiftScript, the same idea but for Swift itself.

It’s exactly that. Real Swift syntax, walked by a tree-walking interpreter, no LLVM, no codegen, no Process/fork/exec — meant for the places where Swift as a compiled binary isn’t an option.

After this success with an AST for bash, I figured, let’s up the game and try the same with Swift Syntax. My Claude Opus has proven time again that it has the necessary tenacity to make any stupid idea come true.

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