A Philosophy of Software Design

[Basile B.]

On Sunday, 24 May 2026 at 06:49:28 UTC, Richard (Rikki) Andrew 
Cattermole wrote:
> On 24/05/2026 4:10 PM, Walter Bright wrote:
>> Invalid code nodes are replaced with "Error" nodes. This 
>> worked far better than I anticipated. No exceptions are 
>> thrown. It also behaves like NaN.
>
> That's not actually how you handled it, although I'm sure it 
> solved some problems much more easily.
>
> You handled it by checking the error count. In other words a 
> global flag.
>
> https://github.com/dlang/dmd/blob/3c2ad72ad3be9c38c76569ccd1574e39fec2256d/compiler/src/dmd/typesem.d#L4787
>
> https://github.com/dlang/dmd/blob/3c2ad72ad3be9c38c76569ccd1574e39fec2256d/compiler/src/dmd/globals.d#L368
>
> If you can get an error node without an error message that is 
> an ICE that should have been emitted but wasn't.

I think a better example is when in expsema the type of an 
expression is set to Terror.

1. This avoids plenty of null checks
2. This poisons the AST, so that, for example, further 
conversions wont pass

What you put links on is rather the system used for error 
recovery. Generally I find that error gagging is clumsy but that 
is casually required (`__traits(compiles)`, `typeof()`, selection 
in an overload set, SFINAE, etc.)

But finally I dont really see how exceptions are related to 
compiler errors. I've never seen a compiler using them for 
notifying invalid input code. Invalid input code is unrelated to 
compiler "as a software" errors (e.g a input file that does not 
exist).