cst {lobstr}

Call stack tree

Description

Shows the relationship between calls on the stack. This function combines the results of sys.calls() and sys.parents() yielding a display that shows how frames on the call stack are related.

Usage

cst()

Examples

# If all evaluation is eager, you get a single tree
f <- function() g()
g <- function() h()
h <- function() cst()
f()

# You get multiple trees with delayed evaluation
try(f())

# Pay attention to the first element of each subtree: each
# evaluates the outermost call
f <- function(x) g(x)
g <- function(x) h(x)
h <- function(x) x
try(f(cst()))

# With a little ingenuity you can use it to see how NSE
# functions work in base R
with(mtcars, {cst(); invisible()})
invisible(subset(mtcars, {cst(); cyl == 0}))

# You can also get unusual trees by evaluating in frames
# higher up the call stack
f <- function() g()
g <- function() h()
h <- function() eval(quote(cst()), parent.frame(2))
f()