Feature Request: Compiler Warning Messages

[Durbatuluk1701]

It would be a nice feature of the CakeML compiler for it to provide warning messages during compilation of possibly unintended behaviors.
 
Example:

fun is_upper_X str =
  let 
    val uppX = "X" 
    val lowX = "x" 
  in
    case str of
      uppX => True
    | lowX => False
  end
    
val () =
  let 
    val _ = TextIO.print (Bool.toString (is_upper_X "X"))
    val _ = TextIO.print "\n"
    val _ = TextIO.print (Bool.toString (is_upper_X "x"))
    val _ = TextIO.print "\n"
  in
    ()
  end

Running it will return

True
True (* Possibly unexpected behavior *)

I believe it would be beneficial for the compiler to give the user a warning such as Pattern "lowX" is redundant in this clause.

[myreen]

I agree that such warning messages are desirable.

However, the CakeML compiler doesn't really have a facility for generating warnings in general at the moment. I think this issue should be generalised to be about making the CakeML compiler generate warning messages and the example above could be one such warning message.

[Durbatuluk1701]

That does seem like a good generalization, I can change the issue title and maybe add more information.