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Leo Razoumov wrote:
On 11/21/08, KHMan <> wrote:
Leo Razoumov wrote:

On 11/20/08, Matthew Paul Del Buono <> wrote:

Hi list,


 I see that it should be executing the line "return (h(op1, op2))" but
that's not what I seem to get in response. I would expect "true" to be the
result if the manual stated "return not not (h(op1, op2))" but it doesn't.
 Is this a manual problem, a Lua problem, or am I missing something?

Apparently, the manual and the actual Lua implementation do differ.

In the function "luaV_equalval" defined in  "lvm.c" the last two line are

 callTMres(L, L->top, tm, t1, t2);  /* call TM */
 return !l_isfalse(L->top);

that essentially mean "return not not (h(op1, op2))" as you correctly
It is different from the pseudo-code in the manual. I would suggest to
correct the manual.

 luaV_equalval needs to return a boolean 0 or 1 for comparison with the
boolean value in field A in the OP_EQ opcode implementation. This is a
straight int comparison, so a 0 or 1 value is mandatory. So in the manual,
the pseudo-code's return type of boolean is implicit.

Yes, in C-code it has to be 1 or 0. This is precisely the reason, why
the Lua manual should be more specific about explicitly mentioning the
cast from h(op1,op2) to the boolean value. IMHO, the way manual has it
now contradicts to the actual Lua implementation.

Heh, there a danger in jumping into the middle of a discussion. :-) I've looked at Matthew's post.

The == operator is always going to return a boolean. The reference manual doesn't say otherwise, or allow modified behaviour. Thus, that is implicit. I would never assume a==b can ever return anything other than a boolean.

Now the metatable function can return anything it wants, but when hooked in to use TM_EQ, it is always going to follow the defined == operator semantics and return a boolean. Since the user is supposed to know that the result is always coerced into a boolean... oh well, perhaps some cognitive adjustment on the part of the user would be helpful.

Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia