I like to use Claude Code to write deterministic computer programs for me, which then perform the actual work. It saves a lot of time.

I had a big backlog of "nice to have scripts" I wanted to write for years, but couldn't find the time and energy for. A couple of months after I started using Claude Code, most of them exist.

I'm a co-founder of Calcapp, an app builder for formula-driven apps using Excel-like formulas. I spent a couple of days using Claude Code to build 20 new templates for us, and I was blown away. It was able to one-shot most apps, generating competent, intricate apps from having looked at a sample JSON file I put together. I briefly told it about extensions we had made to Excel functions (including lambdas for FILTER, named sort type enums for XMATCH, etc), and it picked those up immediately.

At one point, it generated a verbose formula and mentioned, off-handedly, that it would have been prettier had Calcapp supported LET. "It does!", I replied, "and as an extension, you can use := instead of , to separate names and values!") and it promptly rewrote it using our extended syntax, producing a sleek formula.

These templates were for various verticals, like real estate, financial planning and retail, and I would have been hard-pressed to produce them without Claude's domain knowledge. And I did it in a weekend! Well, "we" did it in a weekend.

So this development doesn't really surprise me. I'm sure that Claude will be right at home in Excel, and I have already thought about how great it would be if Claude Code found a permanent home in our app designer. I'm concerned about the cost, though, so I'm holding off for now. But it does seem unfair that I get to use Claude to write apps with Calcapp, while our customers don't get that privilege.

(I wrote more about integrating Claude Code here: https://news.ycombinator.com/item?id=45662229)

I've been using Claude Code a lot lately, and I've been thinking of integrating it into our SaaS tool (a formula-driven app designer). I've been holding off primarily because I've been afraid of the cost (we're not making much money off our $9/mo. customers as it is, and this definitely wouldn't help that).

However, it's becoming clear to me that individual apps and websites won't have their own integrated chatbots for long. They'll be siloed, meaning that they can't talk to one another -- and they sure can't access my file system. So we'll have a chatbot first as part of the web browser, and ultimately as part of the operating system, able to access all your stuff and knowing everything about you. (Scary!)

So the future is to make your software scriptable -- not necessarily for human-written scripts, but for LLM integration (using MCP?). Maybe OLE from the nineties was prescient?

Short-term, though, integrating an LLM would probably be good for business, but given that I'm our only engineer and the fact that our bespoke chatbot would likely become obsolete within two years, I don't think it would be worth the investment.

Other apt comparisons to what I'm building include HyperFormula and Microsoft Power Fx.

No, not really. GoRules appears to be a decision engine that allows non-technical users to define rules visually through a graphical interface. Engineers can then interpret and evaluate these rules using provided libraries.

What I'm building is a formula engine that validates, compiles, and evaluates Excel-like formulas. Compared to GoRules, it’s more akin to the ZEN expression language component than to the broader GoRules system.