Re: Localized precedence declarations

[Michiel Helvensteijn]

On Tuesday 23 June 2009, Hans Aberg wrote:

> The problem has not been resolved, and the type of grammar constraint
> precedences I made are not implemented.
>
> One way to implement it is to not resolve the operator precedences in
> the grammar, but in the actions. This is the only way in the case the
> operator precedences are set dynamically. One program that uses (or so
> I remember) this approach is Hugs <http://haskell.org/>.

That is far too drastic a measure. The operator precedences in my language are 
static. I just need a way to isolate the different groupings of precedence 
declarations, so that no shift/reduce conflict is resolved by two 
declarations from different groupings.

Take this example:

%nonassoc IF_THEN_RULE
%nonassoc "else"

%left '+' '-'
%left '*'

It generates the following relative orders:

IF_THEN_RULE < "else"
IF_THEN_RULE < '+'
IF_THEN_RULE < '-'
IF_THEN_RULE < '*'
"else" < '+'
"else" < '-'
"else" < '*'
'+' < '*'
'- < '*'

But I would prefer if only the following relations were understood:

IF_THEN_RULE < "else"
'+' < '*'
'- < '*'

All the others were unintentional, and might silently (and badly) resolve a 
shift/reduce conflict that I introduced by accident.

-- 
Michiel Helvensteijn
address@hidden