In message <[EMAIL PROTECTED] >, Patrick M
aier writes:
> I have encountered a bug using the Hugs module STArray.
> When reading in the following lines
>
> > import STArray
>
> > test :: ST s Int
> > test = newArr (1,8) 0 >>= (\nums ->
> > writeArr nums 5 42 >>= (\_ ->
> > readArr nums 5 >>= (\v ->
> > return v)))
>
> and then calling
>
> runST test
>
> Hugs 1.4 responds with
>
> ERROR: Type error in encapsulation
> *** expression : runST test
> *** term : test
> *** type : ST a Int
> *** does not match : ST b Int
>
> Using Hugs 1.3 to do the same I get the expected result
>
> 42
>
> I suspect there are bugs in type inference
>
> Find them and kill them!
>
> Patrick Maier
> [EMAIL PROTECTED]
The reported trouble was already found in 970203. Included is a plausible
patch I've been using since then. If you don't like the behaviour, you may
disable the effect of the patch by replace #if 0 with #if 1.
Note (1): Of course, this is _not_ an official patch. This may help you
only if you are so urge that you cannot wait for an official one.
Note (2): Applying the diff. of type.c relaxes the encapsulation criterion.
After that, you will have
ST> :type runST (return 30)
runST (return 30) :: Num a => a
instead of a type error. If you don't like this behaviour, disable
the effect of this part as described above.
Hope this helps.
-----
Yoshihiko Ichikawa, Dept of Info Sci, Fac of Sci, Ochanomizu University
Phone: +81-3-5978-5708 (Dial-in) / +81-3-5978-5704 (Library of Department)
Fax: +81-3-5978-5898 (Faculty) / +81-3-5878-5705 (Library of Department)
E-mail: [EMAIL PROTECTED]
============%< ========================================================
*** preds.c.orig Wed May 28 10:35:40 1997
--- preds.c Wed May 28 10:35:25 1997
***************
*** 271,279 ****
--- 271,294 ----
numFixedVars = 0;
if (anyGenerics(t,o)) { /* contains generic*/
+ #if 0
tl(preds) = qs;
qs = preds;
evids = cons(haskSimp(c,t,o),evids);
+ #else
+ Cell saveHpreds = hpreds;
+ Cell ev = haskSimp(c,t,o);
+ if (saveHpreds == hpreds) {
+ /* constant */
+ Cell d = makeDictFor(ev,NIL);
+ fst(thd3(pi)) = mkSelect(0);
+ snd(thd3(pi)) = d;
+ } else {
+ tl(preds) = qs;
+ qs = preds;
+ evids = cons(haskSimp(c,t,o),evids);
+ }
+ #endif
}
else if (numFixedVars>0) { /* only fixed vars */
tl(preds) = ps;
*** subst.c.orig Tue Mar 11 03:46:02 1997
--- subst.c Wed May 28 10:37:35 1997
***************
*** 273,281 ****
--- 273,295 ----
case TYCON :
case TUPLE : return;
+ #if 0
case AP : markType(fst(t),o);
markType(snd(t),o);
return;
+ #else
+ # if LAZY_ST
+ case AP : if (fst(t) != typeST) {
+ markType(fst(t),o);
+ markType(snd(t),o);
+ }
+ return;
+ # else
+ case AP : markType(fst(t),o);
+ markType(snd(t),o);
+ return;
+ # endif
+ #endif
case OFFSET : markTyvar(o+offsetOf(t));
return;
*** type.c.orig Wed Apr 9 08:26:54 1997
--- type.c Wed May 28 10:48:07 1997
***************
*** 828,833 ****
--- 828,834 ----
savePreds = elimConstPreds(line,savePreds);
markTyvar(beta+1);
tyvarType(beta);
+ #if 0
if (nonNull(preds) || typeIs!=var || tyvar(typeOff)->offs==FIXED_TYVAR) {
Int alpha = newTyvars(2);
Type actual = copyType(typeSTab,beta);
***************
*** 837,842 ****
--- 838,854 ----
reportTypeError(line,snd(e),e,enc,actual,copyType(typeSTab,alpha));
}
preds = savePreds;
+ #else
+ if (typeIs!=var || tyvar(typeOff)->offs==FIXED_TYVAR) {
+ Int alpha = newTyvars(2);
+ Type actual = copyType(typeSTab,beta);
+ bindTv(alpha+1,var,beta+1);
+ if (nonNull(hpreds))
+ actual = ap(QUAL,pair(copyPreds(hpreds),actual));
+ reportTypeError(line,snd(e),e,enc,actual,copyType(typeSTab,alpha));
+ }
+ preds = revOnto(preds, savePreds);
+ #endif
tyvarType(beta+1);
}
#endif
