Porting My 1996 Pascal Calculator to Rust

In his Rails World 2026 keynote DHH talks about one-shot apps built almost instantly with an agent as part of Omarchy. His canonical example is Omacalc, a dead simple calculator. It’s a good demo and not a hard problem. Let’s take it further and rewrite a more advanced calculator in Rust that we can also run as an MCP server, so an AI coding agent can outsource arithmetic to it instead of hallucinating a square root. In 1994 I wrote an expression evaluator for a lab assignment. It grew into Expression Calculator, a shareware Windows app I sold through a company I co-founded, Vestris Inc. In 1997 it got pressed onto a CD-ROM and sold 3,000 copies in Germany under the name Global Calculator. I made money and users wrote fan mail. This week, Copilot and I ported its Pascal/Delphi core to Rust as excalc-rs (crates.io), a CLI and MCP server, in under 24 hours. Both the port and the original are mathematical beasts. They can: Chain 12 comparison and logical/bitwise operators, and 12…

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