say I have a function f as
f = function(x = 1, y, z, t) { x + y + z}
and a list l such
l = list(Y = 2, t = "test")
I can evaluate f in l like
eval(quote(f(y = Y, z = 3)), envir = l)
6
My question is that I'd like to get all the values of the arguments that ends up being used by the function f ie. a function magic that would take a call object and an environment and would return the values of all the arguments that would be used in evaluating the expression.
For instance:
call_obj = quote(f(y = Y, z = 3))
magic(call_obj, envir = l)
# I get a named list which value is list(1,2,3,"test")
# For that matter I do not even need the default arguments values (x)
EDIT: Adding a bounty for a base-r answer (while @Artem Sokolov provided a purrr-rlang one, extracting a couple relevant functions would still be fine though)
tidyverse solution
# Identify the variables in l that can be used to specify arguments of f
args1 <- l[ intersect( names(formals(f)), names(l) ) ]
# Augment the call with these variables
call_obj2 <- rlang::call_modify( call_obj, !!!args1 )
# f(y = Y, z = 3, t = "test")
# Evaluate the arguments of the call in the context of l and combine with defaults
purrr::list_modify( formals(f),
!!!purrr::map(rlang::call_args(call_obj2), eval, l) )
base R solution
# As above
args1 <- l[ intersect( names(formals(f)), names(l) ) ]
# Augment the call with variables in args1
l1 <- modifyList( as.list(call_obj), args1 )[-1]
# Evaluate the arguments in the context of l and combine with defaults
modifyList(formals(f), lapply(l1, eval, l))
Output for both solutions
# $x
# [1] 1
#
# $y
# [1] 2
#
# $z
# [1] 3
#
# $t
# [1] "test"