Syntax with formal semantics makes a lot more sense than ambiguous English prose, especially for something like function signatures. Moreover, logical syntax would allow expressing constraints that are very hard to do with informal prose because logical syntax is much more compact than prose and a lot less ambiguous. Something basic like simply typed predicate logic should be doable for the folks at OpenAI.
Basically, whatever is possible to express with English prose for a computer to execute is always better expressed with formal syntax like lambda calculus. It can still include regular prose but the formal syntax makes it much more clear what is actually intended by the user.
I agree with you. I'm not talking about how it should be, I'm talking about current limitations which are themselves fuzzy and ill-defined. It's reasonable that if they're using plain english instead of a formally defined syntax, it's simply because that works better for now.
Basically, whatever is possible to express with English prose for a computer to execute is always better expressed with formal syntax like lambda calculus. It can still include regular prose but the formal syntax makes it much more clear what is actually intended by the user.