Re: Grammar with low-precedence postfix operator?

Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>For your example involving ^ and ++, I think that one should use
>parentheses explicitly in most cases, e.g. (a^b)++^c or a^(b++)^c.
>You can leave away the parentheses if there is no ambiguity, as in
>your 2++^3, but that's not straightforward to express in BNF.


gcc does something like this


You can say:


if (x & y == 0)


probable error, warn or reject


if ((x & y) == 0)


OK


if (x & (y == 0))


OK, if that's what you want


I don't know how it is implemented.


if (x == 1 && y == 2)


fine IMHO


if ((x == 1) && (y == 2))


too many parens


if (((x >= 1) && (x <= 2)) || ((y >= 1) && (y <= 2)))


way too many parens IMHO, but shouldn't reject


The reason you don't want to reject these is that,
besides that it's style, they could come from macros.


If you color parens in macros, you could also look out for macros:


#define SUM(X, Y) (X)+(Y)


probable error


#define DOUBLE(X) (2*X)


probable error

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