Nest shinyDownloadHander() within a function

I have a code block like so:

output$downloadTransactions <- downloadHandler(

    filename = function() {
        paste('transactions', Sys.Date(), '.csv', sep='')
    },

    content = function(file) {
        write.csv(transactions_table, file)
    }
)

This creates a download button on one of my tables shown by my shiny app and it works as is. In this case it's for downloading transaction data, but I have other metrics I would like the user to be able to download, including sessions and revenue.

Since I make several calls to downloadHandler(), each with minimal variation (metric name and the data frame to be downloaded), I wanted to attempt to write it as a function.

Tried:

# for download button
downloadTable <- function(metric, table) {
  file = function(m) paste(m, Sys.Date(), '.csv', sep = '')
  cont = function(table) write.csv(table, file)
  downloadHandler(
    filename = file(metric),
    content = cont(table)
  )
}

But when I run this as a Shiny app:

output$downloadRevenue <- downloadTable("revenue", revenue_table)

(Note revenue_table is a data frame)

Warning: Error in ==: comparison (1) is possible only for atomic and list types
  86: force
  85: map$set
  84: self$downloads$set
  83: shinysession$registerDownload
  82: origRenderFunc
  81: output$downloadRevenue
   1: runApp

Something I struggle to follow in downloadHandler() is where it gets the variable 'file' from. It's not defined when I call it above in my first code block, yet it magically works. I think it's this piece that is causing my issues.

How can I make shiny::downloadHandler a custom function that takes two arguments, one 'metric', a string defining the name of the metric that the download table is for and then 2, the part that I think is tripping me up, the file?