F#

F* is a general-purpose, proof-oriented language: code can carry specifications that a verifier checks. Its appeal is not replacing ordinary programming, but making high-assurance pieces of a system expressible in the same development workflow.

An essay walks through making 'parse, don't validate' work in TypeScript, where structural typing means a validated Email is indistinguishable from any string. The fix is a branded type: a phantom symbol that makes Email incompatible with string at compile time and vanishes at runtime.

The thread's senior voices split on whether that's the real idea or a fake-out: one argued branding just labels a string as 'validated,' while another countered that all type guarantees are ultimately validation the compiler agrees to trust.