Re: "Circumfix" operators

Joachim Durchholz wrote:
>
> I need to read up on ways to extend operator-precedence parsing to
> "circumfix" operators such as (...), [...], if...then...else... etc.


For parens and brackets you want to stack the left one immediately when
you see it and have the matching right one remove it from the stack. I
tend to do this by having a different priority value for operators when
you first see them than when they are on the stack (other ways also
work, of course). I do the same thing with the virtual
start-of-expression and end-of-expression operators.


As for if-then-else, I wouldn't add them to expression parsing unless
they are really valid in expressions, as they were in Algol or are now
in Xpath. Otherwise, I'd use a recursive descent parser for most of the
language and switch to operator precedence parsing just for expressions.


jeff

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