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the behavior of operator (inplace operator & binary operator)

sbkuizlzl

Hi all.

I'm using Virtuoso IC6.1.8-500.19 and my SKILL script returns unintended results when I use the inplace operator (+=, in my case).

A toy example of the case is as below.

a = 1

b = 3

c = 2

a += b - c

In this case, the expected value of 'a' is 2, I think, but the actual value is 4.

I checked the operation by SKILL IDE and I found that it is translated as (a = (a + b)) - c.

I know that I can get the intended value if I change the line 4 to a += (b - c), but I wonder this unexpected result comes from the nature of SKILL language, which is unlike any other programming languages.

Furthermore, when the binary operator is used with no blank with the secondary argument, it also returns unexpected value.

a = b - c    ; the value of a is 1

a = b-c      ; the value of a is 1

a = b -c     ; the value of a is 3

The last operation treats '-' operator as unary, I think, and it also differs from my expectation.

Will these behavoir be fixed later or is it just the rule for the SKILL?

I cannot find the guideline of it in the SKILL manual.

Thanks.

  • For the first issue, I agree, the inplace operators have the wrong precedence (strictly speaking the issue is that they appear to be left-to-right associative rather than right-to-left like the assignment operator, =). There's an existing CCR for this, 2132643 (filed by one of my team). Perhaps you should contact customer support and request a duplicate be filed. The challenge with fixing this, however, will be that doing so would break existing code that depends on the incorrect precedence.

    The second issue is expected. This is because SKILL doesn't have syntax to mark the end of a statement (e.g. like ";" in C), and so you can have multiple statements on the same line. If you do that, then the last statement is actually two statements, a=b and -c, with the overall return value (e.g. if used at the end of a function) being the -c. Given that you can do "a = b c = d" and that's valid, it would be rather hard to know your intent - so the multiple statements on a single line wins. You just have to be careful with whitespace in SKILL - it's not C (it's a LISP really, and the infix operators are designed to make it more C-like).

    Regards,

    Andrew

  • in reply to Andrew Beckett

    Andrew:

    Thank you for your quick response!

    I will use the inplace operators more carefully (with parenthesis), rather than submit a duplicate request. Slight smile

    And I didn't notice that multiple statements can be in a single line separated by blank! It's the issue that I'm familiar with C language but not with LISP.

    Thanks.

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