PROBLEM

I have the following script where I am using the export function from BSgenome package to write only the first seven chromosomes of an object (of class BSgenome) into separate files.

source("https://bioconductor.org/biocLite.R")
biocLite("BSgenome.Scerevisiae.UCSC.sacCer3")
library(BSgenome.Scerevisiae.UCSC.sacCer3)
library(BSgenome)
    
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrI, "Scerevisiae_chr1.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrII, "Scerevisiae_chr2.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrIII, "Scerevisiae_chr3.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrIV, "Scerevisiae_chr4.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrV, "Scerevisiae_chr5.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrVI, "Scerevisiae_chr6.fasta", compress=FALSE)
export(BSgenome.Scerevisiae.UCSC.sacCer3::Scerevisiae$chrVII, "Scerevisiae_chr7.fasta", compress=FALSE)

The problem is that I have many other organisms for which I must do the same.

OBJECTIVE

How can I automate the export process in a way that the filename of the output matches the object and element used?

So as an example, when Scerevisiae$chrVII is exported, I want to see Scerevisiae_chrVII.fasta for the name of the FASTA file.

WHAT I HAVE TRIED AND HAS NOT WORKED

BiocGenerics::sapply(X = Scerevisiae, MARGIN = c(1:7), 
    function(x) BSgenome::export(con = paste0(substitute(x), ".fasta")))

BiocGenerics::sapply(X = Scerevisiae, FUN = export)

bsapply(new("BSParams", X = Scerevisiae, FUN = function(x) BSgenome::export(con = paste0(substitute(x), ".fasta"))))

> dontprint <- lapply(grep("chr", names(Scerevisiae), value = TRUE), function(x) BSgenome::export(Scerevisiae[[x]], paste0("Scerevisiae_", x, ".fasta")))

> dir(".", ".fasta$")
 [1] "Scerevisiae_chrI.fasta"    "Scerevisiae_chrII.fasta"  
 [3] "Scerevisiae_chrIII.fasta"  "Scerevisiae_chrIV.fasta"  
 [5] "Scerevisiae_chrIX.fasta"   "Scerevisiae_chrM.fasta"   
 [7] "Scerevisiae_chrV.fasta"    "Scerevisiae_chrVI.fasta"  
 [9] "Scerevisiae_chrVII.fasta"  "Scerevisiae_chrVIII.fasta"
[11] "Scerevisiae_chrX.fasta"    "Scerevisiae_chrXI.fasta"  
[13] "Scerevisiae_chrXII.fasta"  "Scerevisiae_chrXIII.fasta"
[15] "Scerevisiae_chrXIV.fasta"  "Scerevisiae_chrXV.fasta"  
[17] "Scerevisiae_chrXVI.fasta"
>