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digitalmars.D.bugs - [Issue 5750] New: Allow pure functions to have lazy arguments

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5750

           Summary: Allow pure functions to have lazy arguments
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: clugdbug yahoo.com.au


--- Comment #0 from Don <clugdbug yahoo.com.au> 2011-03-18 17:34:21 PDT ---
Any function marked as pure, which has a lazy parameter, should be considered
to be weakly pure. Since a lazy parameter is a delegate, there are no limits on
what it can potentially do, so the purity of the function will depend entirely
on the purity of the lazy parameter.

Secondly, when using a lazy parameter, it should be assumed to be adequately
pure, since it was checked when it was constructed.


PATCH:
mtype.c, line 5042, void TypeFunction::purityLevel()

            size_t dim = Parameter::dim(tf->parameters);
            for (size_t i = 0; i < dim; i++)
            {   Parameter *fparam = Parameter::getNth(tf->parameters, i);
                if (fparam->storageClass & STClazy)
                {
-                    /* We could possibly allow this by doing further analysis
on the
-                     * lazy parameter to see if it's pure.
-                     */
-                    error(0, "cannot have lazy parameters to a pure
function");
+                    tf->purity = PUREweak;
+                    break;
                }
                if (fparam->storageClass & STCout)

expression.c, line 7155, CallExp::semantic()
----
            if (sc->func && sc->func->isPure() && !tf->purity)
            {
+                if (e1->op == TOKvar && ((VarExp *)e1)->var->storage_class &
STClazy)
+                {   // lazy paramaters can be called without violating purity
+                    // since they are checked explicitly
+                }
+                else
                error("pure function '%s' cannot call impure delegate '%s'",
sc->func->toChars(), e1->toChars());
            }
            if (sc->func && sc->func->isSafe() && tf->trust <= TRUSTsystem)
            {
                error("safe function '%s' cannot call system delegate '%s'",
sc->func->toChars(), e1->toChars());
            }

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next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
           Severity|normal                      |enhancement


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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com


--- Comment #1 from Jonathan M Davis <jmdavisProg gmx.com> 2011-03-18 17:53:22
PDT ---
I definitely like this idea, but I am a bit worried that it will be somewhat
buggy if integrated at present. I believe that there are at least a couple of
bugs (such as bug# 3833 ) related delegates not dealing with attributes such as
const and pure properly, and you can end up with attributes being ignored when
they shouldn't be. That doesn't necessarily mean that this shouldn't be
integrated right now, but it _does_ mean that the result could be buggy.

I'm sure that Don has a far better understanding of all of that sort of
compiler stuff than I do (and perhaps he's taken all of what I've said into
account already), but I thought that I should point out that stuff like const
and pure don't really seem to work properly with delegates, so this enhancement
- while definitely desirable - may not work very well at the moment.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #2 from Don <clugdbug yahoo.com.au> 2011-03-18 23:31:18 PDT ---
(In reply to comment #1)

 I definitely like this idea, but I am a bit worried that it will be somewhat
 buggy if integrated at present. I believe that there are at least a couple of
 bugs (such as bug# 3833 ) related delegates not dealing with attributes such as
 const and pure properly, and you can end up with attributes being ignored when
 they shouldn't be. That doesn't necessarily mean that this shouldn't be
 integrated right now, but it _does_ mean that the result could be buggy.


Bug 3833 is totally unrelated to this. I have looked at all bugs which use the
word "lazy" and none influence this. 
I've also looked at all open bugs which use the word "delegate" and also failed
to find anything which influence this one.
Bug 1818 is more related, but still isn't a problem.

The main reason that none of those existing bugs cause problems is that
enhancement bug 809 has NOT been accepted and "fixed". This means that although
'lazy' is internally implemented using delegates, there are very few places in
the compiler where that fact is exposed. It stays as a lazy parameter almost
all of the time, which isolates it from the other issues.


Also worth noting: the patch fixes bug 5475, and would make fixing bug 5476
trivial.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #3 from bearophile_hugs eml.cc 2011-03-19 05:27:08 PDT ---
(In reply to comment #2)

Thank you for this bug report, Don, I was thinking about opening it.


 Also worth noting: the patch fixes bug 5475,


Do you mean bug 5745?


Also, this helps bug 5746 too.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #4 from Jonathan M Davis <jmdavisProg gmx.com> 2011-06-09 02:28:53
PDT ---
Where does the situation with this bug currently stand? Would it be at all safe
at this point to put this patch (or a fixed up version of it if it's too old)
into dmd and finally make functions which take lazy parameters able to be pure?
This would be a huge gain for enforce in particular.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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kennytm gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kennytm gmail.com


--- Comment #5 from kennytm gmail.com 2011-07-10 03:18:30 PDT ---
DMD pull #227.

https://github.com/D-Programming-Language/dmd/pull/227

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Jul 10 2011
prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


--- Comment #6 from Walter Bright <bugzilla digitalmars.com> 2011-08-11
22:51:17 PDT ---
https://github.com/D-Programming-Language/dmd/commit/b6dead3be11cc44265cd4288549fcd114a127768

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