Incomplete pattern matching in nested patterns

[tknawara]

Hi team,

I'm new to F#, so apologies if this was raised before or if I'm doing something wrong in the pattern matching construction.

I have a simple AST for expressions. Nothing fancy, Binary/Unary expressions and each expression has an operator and operands.
Now, I'm attempting a pattern match, where I want to match on binary expressions where the operand is say Divide and remainder, I'm doing something like this

Now op in this branch should only be Divide or Remainder, so further matching on it should be exhaustive, but for some reason I'm getting a warning about incomplete pattern.

[brianrourkeboll]

Hi, welcome to F#! This isn't the right place for this issue, though. (This repository is for suggesting new language features.)

For compiler bugs, you want https://github.com/dotnet/fsharp/issues.

For questions/discussion, you want Discord, Slack, or perhaps https://github.com/dotnet/fsharp/discussions.

I would need to see the definition of IR_Ast.BinaryOperator, but if it has more cases than just Divide and Remainder, then that explains what you are seeing. If you are expecting the outer match on (Divide | Remainder) to narrow the typing for the inner match, F# does not do that (unlike, say, TypeScript). Any given match on a union will need to handle all cases.

[tknawara]

@brianrourkeboll Thanks for the links and apologies for opening the issue in the wrong repository. Your explanation make sense.