Re: Simple Expression Recursion vs Expression/Term/Factor

Hi,


The grammar
expr -> expr + expr | expr * expr | id | num
is an ambiguous one. For example, for the string "id + id * id", it generates
two different parse trees.


On the other hand, the grammar involving term, factor is an umambiguous one. It
generates a unique parse tree for the above string.


By the way, if you are using yacc, you can resolve the ambiguity in first case
by giving precedences to "+" and "-" using %prec.


-Vinay Kakade.


Mike Stogden wrote:


> Please could someone offer an explanation as to the relative merits of
> describing expressions as productions based on two comparable
> specifications?
>
> I have seen expressions for the same language described as...
>
> expr -> expr + expr
> expr -> expr * expr
> etc...
>
> alternatively...
>
> expr -> expr + term
> term -> factor | term * factor
> factor -> number | identifier
> etc...

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