r - Make result in tryCatch expr available to warning handler -

in usual implementation of trycatch, warning handler returns custom value, e.g.

trycatch(expr,   warning = function(w) { print(w) ; return(null) } 

what if want warning handler return result of expr without running expr again? (the reason expr api call cuts limit.) tried

trycatch({res <- expr; return(res)},       warning = function(w) { print(w) ; return(res) } 

but of course doesn't work because res not available in warning handler.