[haXe] Boolean statements type error

[Tommy Olesen]

Dear Nicolas,

I suggest haxe consider a Bool statement a type error.  This will
catch bugs like this one:

if (rs == null) {
    rs == [];
}

that I just spent some time finding.  Because I am such a fast typer
;-) there are too many ='s in the example above.  This is a variant of
a classical bug: one = too little in an if:

  var x : Bool;
  var y : Bool;
  if (x = y) {

causing the comparison to be seen as an assignment that happens to
return a Bool.

I realise that SOME Bool statements must be allowed, e.g.,

    return if (ok) a || b else {trace('oh no, there was an error'); false;}

I also realise in some cases you do want to execute a statement for
its side effects and throw away the value, e.g., call a function that
returns Bool.  In that case, however, the programmer can make a dummy
variable assignment.

There is a trade off between expressivity in a type system and its
ability to predict errors.  In this case, I think more programmer time
has been wasted in this world debugging too few or too many ='s than
has been wasted from lack of expressivity in languages that outlaw
this.


Kind Regards,
Tommy