Re: variable lookahead in cup? Please help. (Hans Aberg)
23 Aug 2003 23:10:48 -0400

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Re: variable lookahead in cup? Please help. (2003-08-23)
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From: (Hans Aberg)
Newsgroups: comp.compilers
Date: 23 Aug 2003 23:10:48 -0400
Organization: Mathematics
References: 03-08-063
Keywords: parse
Posted-Date: 23 Aug 2003 23:10:48 EDT (Martin) wrote:

>I am trying to write a Paser for a simple language. I'd like it to parse
>the expression 'STRING = STRING & STRING' like STRING = (STRING &

This seems to be poor practise, as in the first case & has higher
precedence than =, and in the other case, it is the reverse. It is better
to keep precedences fixed, if possible. Even though I recently found a
funny exception:

In a proof verification language I use the both cases
        all x A
        all x: <formula>
Here, the first case is the traditional notation, but it requires on to
use a lot of parenthesizes, which looks heavy in a language. So I
introduced the second one. It then turns out that the two operators "all
x" and "all x:" have different precedences.

But you can see the language design criteria I use. Also, the two
different precedences have different notational forms.

    Hans Aberg * Anti-spam: remove "remove." from email address.
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