Please take this to python-ideas. On Fri, Mar 27, 2009 at 2:15 PM, Joe Smith <unknown_kev_cat@hotmail.com> wrote:
Jared Grubb wrote:
I'm not a EBNF expert, but it seems that we could modify the grammar to be more restrictive so the above code would not be silently valid. E.g., "++5" and "1+++5" and "1+-+5" are syntax errors, but still keep "1++5", "1+-5", "1-+5" as valid. (Although, '~' throws in a kink... should '~-5' be legal? Seems so...)
So you want something like u_expr :: = power | "-" xyzzy_expr | "+" xyzzy_expr | "\~" u_expr xyzzy_expr :: = power | "\~" u_expr
Such that: 5 # valid u_expr +5 # valid u_expr -5 # valid u_expr ~5 # valid u_expr ~~5 # valid u_expr ~+5 # valid u_expr +~5 # valid u_expr ~-5 # valid u_expr -~5 # valid u_expr +~-5# valid u_expr
++5 # not valid u_expr +-5 # not valid u_expr -+5 # not valid u_expr --5 # not valid u_expr
While, I'm not a python developer, (just a python user) that sounds reasonable to me, as long as this does not silently change the meaning of any expression, but only noisily breaks programs, and that the broken constructs are not used frequently.
Can anybody come up with any expressions that would silently change in meaning if the above were applied?
Obviously a sane name would need to be chosen to replace xyzzy_expr.
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