[jkhdigital]

I’d suggest that they are in fact the same thing, and differ only in the level of formality... somewhat akin to the difference between machine code and interpreted scripts.

[skybrian]

An informal spec is about getting your intention across to humans who will interpret it in some reasonable way and fill in any gaps. It’s not math or a computer program at all.

David Chapman makes a distinction between rational and reasonable behavior, and it’s more like his “making breakfast” example:

https://metarationality.com/reasonableness-aspects

[gugagore]

Both machine code and interpreted scripts are executable, and so they have a formal meaning, at least for a given machine or interpreter.

They both feel as "formal" as the other, and much more so than a spec written in e.g. English.