Comment author: @gasche

Having a warning in that case would be fine, and it could be enabled by default¹. I'm not convinced it is a good idea to make it an error, as it could break code for no excellent reason.

¹: such code always raises warning 27, "unused variable", but this warning is not enabled by default as it would be too noisy for some codebases.

The reason this should remain allowed is that it is a natural consequence of currification: "let f = fun x -> fun x -> x" shadows a first variable of name "x" with another of name "x".

Comment author: @bobzhang

let f = fun x -> fun x -> ... would probably be a bug

let f = fun x -> let y = 32 ... in fun x -> ... this seems to be good

can we have a warning for duplicated parameters which is more server than unused varaibles

Comment author: @lefessan

I am not convinced by the use-case: when you generate the Javascript, you can check if the variables have the same name, and change the name of the unused one (to "x_unused_1", anyway, you won't need to debug it, as it is unused).

Comment author: @garrigue

I'm closing this one, as it is a duplicate of #4904.
People who want to discuss should do it there.