def comp-to-png [] {
    glob *.pdf | each { |x| $x | path relative-to $"(pwd)"  }
}
# convert (a pdf) to png
export def "to png" [pattern:string@comp-to-png] {
    glob $pattern | each {|pdf| 
       let dest = ($pdf | path parse | update extension png | path join)
       ^convert -density 300 $pdf $dest
       $dest
    }
}