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Obtain all the undefined variables in an expression
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| find_unbound <- function(lang) { | |
| stopifnot(is.language(lang), !is.expression(lang)) | |
| bound <- character() | |
| unbound <- character() | |
| rec_fun <- function(lang) { | |
| if(is.call(lang)) { | |
| # These are assignment calls; if any symbols are assigned and have | |
| # not already been found in a leaf, they are defined as bound | |
| if((lang[[1]] == as.name("<-") || lang[[1]] == as.name("="))) { | |
| for(i in as.list(lang)[-(1:2)]) Recall(i) | |
| if(is.name(lang[[2]]) && !as.character(lang[[2]]) %in% unbound) | |
| bound <<- c(bound, as.character(lang[[2]])) | |
| } else for(i in as.list(lang)[-1]) Recall(i) | |
| } else if (is.name(lang) && ! as.character(lang) %in% bound) | |
| # this is a leaf; any previously bound symbols are by definition | |
| # unbound | |
| unbound <<- c(unbound, as.character(lang)) | |
| } | |
| rec_fun(lang) | |
| unique(unbound) | |
| } | |
| file_unbound(lang) |
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As defined in this StackOverflow question: http://stackoverflow.com/questions/32363338/how-to-obtain-all-the-variables-that-need-to-be-defined-prior-evaluating-an-expr/32365609#32365609