search for: expr_or_assign

Hello I was reading the source main/src/gram.y and had one question, how does R parse x = 1 According the grammar: prog : END_OF_INPUT { return 0; } | '\n' { return xxvalue(NULL,2,NULL); } | expr_or_assign '\n' { return xxvalue($1,3,&@1); } | expr_or_assign ';' { return xxvalue($1,4,&@1); } | error { YYABORT; } ; So this should be of the 3rd form. Also, the expr_or_assign is of the 2nd form in expr_or_assign : expr { $$ = $1; }...

...from f(a<-b).) Other tokens which have lower precedence than assignments are flow-control items, IF ELSE WHILE FOR REPEAT, but I don't see any way to confuse them in the same way as '?'. It might be possible to resolve the situation by specifying '?' syntax explicitly as expr_or_assign '?' expr_or_assign, but, well, "There be Tygers here"... -pd > On 30 Aug 2019, at 18:32 , Kevin Ushey <kevinushey at gmail.com> wrote: > > See also: https://bugs.r-project.org/bugzilla/show_bug.cgi?id=16710 > > On Fri, Aug 30, 2019 at 9:02 AM William Dunl...

...function ### is this a bug or desired behavior? Using parenthesis of coures solves the problem. However, I think the operator precedence could be the problem here. I looked at the "./src/main/gram.y" and I think that the line 385 | FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW should be of way higher precedence. But I cannot forsee the side effects of that (which could be horrible in that case). If this is the desired behaviour and not a bug, I'm very interested in the rational behind that. Best wishes, Wilm ps: $ R --version R version 3.3.1 (2016-06...

...desired behavior? Using parenthesis of coures > solves the problem. However, I think the operator precedence could > be the problem here. I looked at the "./src/main/gram.y" and I > think that the line 385 > | FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW > should be of way higher precedence. But I cannot forsee the side > effects of that (which could be horrible in that case). > > If this is the desired behaviour and not a bug, I'm very > interested in the rational behind that. > > Best wishes,...

Precedence is a property of the parser and has nothing to do with the semantics assigned to various symbols. Using just core R functions you can see the precedence of '?' is between those of '=' and '<-'. > # '=' has lower precedence than '?' > str(as.list(parse(text="a ? b = c")[[1]])) List of 3 $ : symbol = $ : language `?`(a, b) $

...gt; is this a bug or desired behavior? Using parenthesis of coures solves the > problem. However, I think the operator precedence could be the problem > here. I looked at the "./src/main/gram.y" and I think that the line 385 > | FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW > should be of way higher precedence. But I cannot forsee the side effects > of that (which could be horrible in that case). > > If this is the desired behaviour and not a bug, I'm very interested in the > rational behind that. > > Best wishes, > > Wilm >...

...a bug or desired behavior? Using parenthesis of coures solves the >> problem. However, I think the operator precedence could be the problem >> here. I looked at the "./src/main/gram.y" and I think that the line 385 >> | FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW >> should be of way higher precedence. But I cannot forsee the side effects >> of that (which could be horrible in that case). >> >> If this is the desired behaviour and not a bug, I'm very interested in >> the rational behind that. >> >> Best...