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On 9/21/2010 8:29 AM, Ryota Hirose wrote:
Hello Lua Hackers,

2010/9/21 KHMan wrote:

        So, source line 1 was compiled to 7 lines binary, line 3 was 8
        lines, line 5 was 9 lines.

    Look closely, why are you counting the RETURN?

I'm sorry, it's my mistake. Last RETURN becomes from whole chunk,
not a single source line.  Exactly, source line 1 was compiled to
7 lines, line 3 and 5 were 8 lines.

    So this is a 'win'? Colour me unimpressed.

The difference between line 1 and 3, a ternary operator and
and/or, is little.  and/or needs one more TEST line (And, this
TEST line is what I want to eliminate by a ternary operator...).

There would not be any noticeable performance difference in normal programs. I think it's better to stick to a discussion on syntax rather than tout a case of one or two instructions saved.

I doubt adding syntax here and there for these reasons is good programming language design.

  But the difference between line 1 and 5, a ternary operator and
if-statement, is big.  With a ternary operator, a
compiler calculated left operand of assignment only once.  But
with if-statement, the left operand must be compiled twice.  When
the left operand is complex, this difference became bigger.

If by 'left operand' you mean the LHS of 'z'? I can't remember any complex variations for assignment other than a list of identifiers.

But look, only one path is executed -- nothing is 'saved' during execution. There would be negligible performance difference.

16 [5] GETGLOBAL 0 -2 ; a
17 [5] TEST     0 0 0
18 [5] JMP       3 ; to 22
19 [5] GETGLOBAL 0 -3 ; b
20 [5] SETGLOBAL 0 -6 ; z
21 [5] JMP       2 ; to 24
22 [5] GETGLOBAL 0 -4 ; c
23 [5] SETGLOBAL 0 -6 ; z

If I were using my VIC-20, then I would applaud such measures of saving an instruction here and there. But with Lua, I don't think these can be used as very good reasons in support of your proposed syntax.

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