Nesting glue function in custom function - r

Question

I want to create a custom log function, that would get used in other functions. I am having issues with the custom function where arguments don't seem to flow through to the inner log function. My custom log function is inspired by the logger package but I am planning to expand this usage a bit further (so logger doesn't quite meet my needs)
log_fc <- function(type = c("INFO", "ERROR"), ...) {
print(
glue::glue("[{type} {Sys.time()}] ", ...)
)
}
Next I am planning to use log_fc in various other custom functions, one example:
test_fc <- function(forecast) {
log_fc(type = "INFO", "{forecast} is here")
#print(forecast)
}
If I test this, I get the following error:
> test_fc(forecast = "d")
Error in eval(parse(text = text, keep.source = FALSE), envir) :
object 'forecast' not found
I am not sure why argument forecast is not being picked up by the inner test_fc function. TIA

Answer 1

You could use the .envir argument:
log_fc <- function(type = c("INFO", "ERROR"), ...) {
env <- new.env(parent=parent.frame())
assign("type",type,env)
print(
glue::glue("[{type} {Sys.time()}] ", ...,.envir = env)
)
}
test_fc <- function(forecast) {
log_fc(type = "INFO", "{forecast} is here")
}
test_fc("My forecast")
#> [INFO 2022-12-18 12:44:11] My forecast is here

Answer 2

There are two things going on.
First, the name forecast is never passed to log_fc. The paste solution never needs the name, it just needs the value, so it still works. You'd need something like
log_fc(type = "INFO", "{forecast} is here", forecast = forecast)
to get the name into log_fc.
The second issue is more complicated. It's a design decision in many tidyverse functions. They want to be able to have code like f(x = 3, y = x + 1) where the x in the second argument gets the value that was bound to it in the first argument.
Standard R evaluation rules would not do that; they would look for x in the environment where f was called, so f(y = x + 1, x = 3) would bind the same values in the function as putting the arguments in the other order.
The tidyverse implementation of this non-standard evaluation messes up R's internal handling of .... The workaround (described here: https://github.com/tidyverse/glue/issues/231) is to tell glue() to evaluate the arguments in a particular location. You need to change your log function to fix this.
One possible change is shown below. I think #Waldi's change is actually better, but I'll leave this one to show a different approach.
log_fc <- function(type = c("INFO", "ERROR"), ...) {
# Get all the arguments from ...
args <- list(...)
# The unnamed ones are messages, the named ones are substitutions
named <- which(names(args) != "")
# Put the named ones in their own environment
e <- list2env(args[named])
# Evaluate the substitutions in the new env
print(
glue::glue("[{type} {Sys.time()}] ", ..., .envir = e)
)
}
test_fc <- function(forecast) {
log_fc(type = "INFO", "{forecast} is here", forecast = forecast)
}
test_fc(forecast = "d")
#> [INFO 2022-12-18 06:25:29] d is here
Created on 2022-12-18 with reprex v2.0.2

Answer 3

The reason for this is that when your test_fc function connects to the log_fc function, the forecats variable wouldn't be able to be found, because it's not a global function; thus, you can't access it from the other function.
The way to fix this is by defining a global variable:
log_fc <- function(type = c("INFO", "ERROR"), ...) {
print(
glue::glue("[{type} {Sys.time()}] ", ...)
)
}
test_fc <- function(forecast) {
forecast <<- forecast
log_fc(type = "INFO", "{forecast} is here")
}
print(test_fc(forecast = "d"))
Output:
d is here

Answer 4

Since you're already using glue you could use another glue::glue in test_fc to accomplish the pass-through, such as:
log_fc <- function(type = c("INFO", "ERROR"), ...) {
print(
glue::glue("[{type} {Sys.time()}] ", ...)
)
}
test_fc <- function(forecast) {
log_fc(type = "INFO", glue::glue("{forecast} is here"))
}
which yields
> test_fc('arctic blast')
[INFO 2022-12-21 15:56:18] arctic blast is here
>