Thanks that's a clear example. What I'm looking for is a name for a pattern where a function returns (typeof ExpectedType | typeof InvalidType). Say it's a pip

Thanks that's a clear example. What I'm looking for is a name for a pattern where a function returns (typeof ExpectedType | typeof InvalidType). Say it's a pipelined compiler and you want all the passes to continue even with InvalidTypes, and then at the end of the pipeline the result is a structure of the correct shape, but there may be some "holes" filled with InvalidTypes. So one way to say it is exception types without the Try/Catch.