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Re: PDD 2: sample add()

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Ken Fox
February 15, 2001 17:56
Re: PDD 2: sample add()
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David Mitchell wrote:
> To get my head round PDD 2, I've just written the the outline
> for the body of the add() method for a hypophetical integer PMC class:

[... lots of complex code ...]

I think this example is a good reason to consider only having one
argument math ops. Instead of dst->add(arg1, arg2) why not just have
dst->add(arg)? Then the PVM can generate code that does the right
thing considering the types of all values in an expression.

It doesn't affect the ability to overload at all -- we just move
overloading to an earlier stage of compilation, i.e. before we emit
PVM instructions.


  Perl code:  $x = 1 + 2
  Parse tree: op_assign($x, op_add(1, 2))
  PVM code:   $x = 1; $x += 2

  Perl code:  $x = 1 + 2 + 3
  Parse tree: op_assign($x, op_add(op_add(1, 2), 3))
  PVM code:   new $t; $t = 1; $t += 2; $x = $t; $t += 3

It will be more work for the optimizer, but I think it will produce
much more understandable PMC objects.

- Ken

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