Re: Recursive descent and left recursion

mfinney@lynchburg.net wrote:
>
> However, I have been using recursive descent with left recursive
> grammers for more than a decade. All it takes is the trivially
> obvious check to allow the left recursion. Take, for example...
>
> (1) <exp> := <exp> + <term>
> (2) <exp> := <term>
>
> when expanding (1), at the first term I simply check to see if the
> current token in the input stream is the same as the last time that
> the rewriting rule was expanded. If it is, then the parse has not
> advanced and you have the infinite loop situation. I simply fail the
> expansion and select an alternate rewriting rule for expansion.


At the risk of appearing thick, I do not see how this works. Surely,
given an expression like "1+2+3+4+5" I have to "pump" out four exp +
terms before I shift the first symbol (the 1) of the expression, so
the method suggested will not parse this expression.


What am I failing to grasp?
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