Puzzling infinite loop in template code

[Andrew Knapp]

I can't figure out why this code loops forever. Is it a bug in the compiler?

#include "share/atspre_staload.hats"
#include "share/atspre_define.hats"

staload UN = "prelude/SATS/unsafe.sats"

abst0ype foo(a:t0ype) = lint
abst0ype twice(a:t0ype) = int

extern fun{a:t@ype} myprint (x: string): void

implement(a) myprint<twice(a)>(x) =
  let
    val f = myprint<a>
  in
    f(x);
    f(x);
  end

implement(a) myprint<foo(a)>(x) =
  begin
    print("foo(");
    myprint<a>(x);
    print(")");
  end

implement myprint<int>(x) = print(x)

implement main0() =
  let
    val x = "LOOP"
  in
    myprint<twice(foo(int))>(x)
  end

[Hongwei Xi]

This is caused by a known tail-call optimization bug.

You can circumvent the bug by adding some do-nothing code:

implement(a) myprint<twice(a)>(x) =
  let
    val f = myprint<a>
  in
    f(x);
    f(x);


    () where { val () = () } // do nothing


  end


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