[MLton] behavior of forceUsed
Thu, 5 Aug 2004 19:21:34 -0400 (EDT)
What do people intuitively believe (or want) the forceUsed annotation to
do in the following situation:
structure X = struct val x = () end
structure Y = struct val y = () end
structure Z : sig val z : unit end
= struct val z = X.x val zz = ()end
ann warnUnused true in
ann forceUsed in
Each of X,X.x,Y,Y.y,Z,Z.z,Z.zz were introduced in the scope of warnUnused
true, so might appear in an unused warning.
There are no bindings in scope at the end of the program.
The only thing that is actually used is X.x, so we certainly should not
get warnings for X or X.x.
I see three choices for what to do in the scope of forceUsed :
1) everything that is introduced in the scope of forceUsed is forced;
Under this scenario, Z, Z.z, and Z.zz will be forced.
Hence, Y and Y.y will be warned as unused.
However, this is really a non-option, as it exactly corresponds to
warnUnused false, so we have a mechanism for acheiving this.
2) everything in the environment scope at the end of the forceUsed scope
is forced to be used. Under this scenario, because Y and Y.y are in
scope for the forceUsed annotation, then they will be forced and
will not be warned. Likewise, Z and Z.z will be forced.
Hence, Z.zz will be warned as unused.
3) everything that was introduced in the scope of the forceUsed and
is in the environment scope at the end of the forceUsed scope
is forced to be used. Under this scenario, only Z and Z.z will be
forced. Hence, Y, Y.y, and Z.zz will be warned as unused.
The current behavior is 2, although I think it would be more natural to
have the behavior be 3. Although, I don't quite know how to implement it.