[nyberg]

The issue isn't as simple as just having better error unions with payloads. Constructing the error diagnostics object needs to be taken into account and the costs it brings (e.g does it allocate? take up a lot of stack space? waste resources when one doesn't need the extra information?). Such is a design choice for the programmer not the language as only they know which approach will be more effective given they have a clear view of the surrounding context.

An alternative is to allow an additional parameter which optionally points to a diagnostics object to be updated upon error. Returning an error here signals that the object contains additional information while not harming composition as much and giving the choice of where to store such information. This is arguably a better pattern in a language where resource allocation is explicit.

[valenterry]

I think what you are saying is pretty orthogonal to what I was saying no?

[rootlocus]

I'm not really experienced with programming language design or with compilers, but it seems to me the design of a systems programming language has to compromise on the side of performance. If the implementation of the design requires additional space or cpu time, it may not be a good fit for the language. As such, it's not orthogonal.