Behavior changes unexpectedly? without a `---`. about dahlia HOT 5 CLOSED

Yeah, that’s the thing I’m clarifying—the dahlia type checker will tell you when you need to put in —- by giving resource usage errors. Everything else is supposed to be the pass’s job.

of course, adding —- is a useful debugging trick when the pass is doing something unexpected.

from dahlia.

Further minimizing the program:

let n: ubit<6> = 4;
let m: ubit<6> = 0;
let i: ubit<6> = 0;

while (m < n) {
  while (i < m) {
    let end: ubit<6> = i + 1;
    let j: ubit<6> = 0;
  }
  m := m + 1;
}

The problem seems to be that the sequentialize pass does not add a --- between while (i < m) { ... } and m := m + 1.

from dahlia.

Thanks for reporting this @cgyurgyik. A good rule of thumb for finding these kinds of issues: if a program type checks without --lower, you should never have to add any "fake" ---. The compiler should do that for you.

Since --- slow down the programs by sequentializing statements, it is always a good idea to minimize them by just running the compiler without --lower. If you run into any more of these, please report them too!

from dahlia.

Thanks for reporting this @cgyurgyik. A good rule of thumb for finding these kinds of issues: if a program type checks without --lower, you should never have to add any "fake" ---. The compiler should do that for you.

Since --- slow down the programs by sequentializing statements, it is always a good idea to minimize them by just running the compiler without --lower. If you run into any more of these, please report them too!

Ok good to know. Here, I initially wasn't sure whether this was part of a pass, or whether it was required by me, the programmer, to place the ---. Hence, the question mark.

from dahlia.

Indeed! To put it ever so slightly differently, --- "should" never affect program semantics, i.e., the output. (Removing --- should never change the output, although it can make a program not type-check. Adding --- to a well-typed program should neither change the output nor cause a type error.) If it does, that's a compiler bug.

from dahlia.