Re: problems with absolute value structure in algebraic grammar

[Frank Heckenbach]

Samad Lotia wrote:

> The purpose of this grammar file is to produce a
> parser which can parse algebraic expressions. The
> purpose of the enclosed_statements rule is to support
> implicit multiplication. For example, the expression:
> 
> 9acos(0.5)
> 
> Really means:
> 
> 9*acos(0.5)
> 
> Or the expression:
> 
> 8|-2|(2^3)
> 
> Really means:
> 
> 8*abs(-2)*(2^3)
> 
> 
> When bison parses this grammar file, it reports a
> shift/reduce conflict at line 22. It, for some reason,
> cannot accept rules like this:
> enclosed_statement: (a_token) statement (same_token)

Your language is ambiguous:

  2|3|4|5|6

could mean

  2 * abs (3 * abs (4) * 5) * 6

or

  2 * abs (3) * 4 * abs (5) * 6

Since the ambiguity is in the language, not the grammar, no amount
of rearranging the grammar or using precedence will save it, unless
you want to make additional restrictions, such as no nested ||
except in () ...

Frank

-- 
Frank Heckenbach, address@hidden
http://fjf.gnu.de/
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