R iGraph graph.bfs and environment -

having trouble running breadth-first search algorithm on graph, current concern environment parameter, callback function evaluated.

this callback function

f.in <- function(graph, data, extra) {     time <- get.vertex.attribute(graph, "time", index=data["vid"])     root_time <- get.vertex.attribute(graph, "time", index=extra)     print(ls(environment()))     if (time != 0){           time_difference <- time - root_time          result_list <- c(list(), time_difference)     } } 

this context functions called

graphs <- decompose.graph(network_graph, max.comps = na, min.vertices = 0)  lapply(graphs, function(g){     v0 <- which(degree(g, mode="out") == 0)     t0 <- get.vertex.attribute(g, "time", index=v0)     if (t0 != 0) {          bfs_environment <- new.env()          assign("result_list", list(), envir=bfs_environment)          graph.bfs(g, v0, neimode="in", callback=f.in, extra=v0, rho=bfs_environment)     } }) 

now print of environment shows me following variables "data" "extra" "graph" "root_time" "time"

the question when have passed environment callback function evaluated, why "result_list" not available? there wrong passing environment? btw using r 2.15.3 , igraph 0.7.0

when documentation states:

rho: environment in callback function evaluated

it means passed environment parent of callback environment.

so can retrieve variable using get() , parent.frame() functions, shown in following example:

mycallback <- function(graph, data, extra) {   print(ls(parent.frame()))   print(get('result_list', envir=parent.frame()))   stop('just stop @ first call...') }  # simple tree 3 nodes g <- graph.tree(3, children = 2, mode='out')  bfs_environment <- new.env() assign("result_list", list(a=3), envir=bfs_environment)  graph.bfs(g, 1, callback=mycallback, extra=null, rho=bfs_environment) 

output:

[1] "result_list" $a [1] 3