On August 23, 2010 01:27:24 pm Philippe Grosjean wrote: > They have to write such a code like this: > > if (x < -3) do_something > > That way, there is no ambiguity. Don't you think it's important to > write clear code, including by using spaces where it makes it easier > to read,... and less ambiguous, as you just realize?
I fully agree, and I'm sure nobody here would dispute your advice. But we all sometimes make typos, and the point here is that the grammar's ambiguity makes for hard-to-find bugs. So, if I may focus us back on the OP's suggestion: "that R simply warn about an ambiguity" in 'if' statement's comparison involving '<-[0-9]'. It doesn't seem like an unreasonable suggestion. For comparison, GCC will do the same thing with C code when the '-Wparentheses' switch if assignment is used in a context where a truth value is expected. (E.g., 'if (x = 3)'.) It's been a very long time since I looked at Yacc and Lex source, but it looks like function 'xxif' in gram.y is the earliest place where we have a whole IF statement. AFAICT, this is evaluated in 'do_if' function of eval.c. There, the condition is evaluated via 'asLogicalNoNA'. Could 'do_if' instead use a function similar to 'asLogicalNoNA' but which issues a warning if the condition is an assignment? Davor ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
