On 04/07/2016 01:24, Lawrence D’Oliveiro wrote:
On Monday, July 4, 2016 at 12:17:47 PM UTC+12, BartC wrote:
On 04/07/2016 01:00, Lawrence D’Oliveiro wrote:
On Monday, July 4, 2016 at 11:47:26 AM UTC+12, eryk sun wrote:
Python lacks a mechanism to add user-defined operators. (R has this
capability.) Maybe this feature could be added.
That would be neat. But remember, you would have to define the operator
precedence as well. So you could no longer use a recursive-descent parser.
That wouldn't be a problem provided the new operator symbol and its
precedence is known at a compile time, and defined before use.
That is how it is normally done. (E.g. Algol 68.)
But you still couldn’t use a recursive-descent parser.
Why not?
The structure of such a parser doesn't need to exactly match the grammar
with a dedicated block of code for each operator precedence. It can be
table-driven so that an operator precedence value is just an attribute.
--
Bartc
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