Stylus Mixin for defining and using webfonts

_fonts.styl

/* Esplaination
****************************************************************************
This include represents a pattern for handling fonts which I have settled on after a lot of time 
struggling to get fonts to render consistently across browsers. The jist of it is this; I don't 
use font-weight or font-style. Instead I use a different font-family for each variation of the 
font (ie. font-family: "FiraSans-Regular"; font-family: "FiraSans-BoldItalic"). The reason I do 
this is that browsers don't always use the appropriate @font-face even when you declare them 
with font-weight and font-size. This method allows me to control EXACTLY which font file is used.
*/

/* Define the names of the font-families and corresponding files
* do not use these variables outside of this file
*****************************************************************************/
$font = "FiraSans";
$fontGeneric = sans-serif;
$fontFamilies = {
  regular: $font + "-Regular",
  bold: $font + "-Bold",
  italic: $font + "-Italic",
  boldItalic: $font + "-BoldItalic"
};

/* font() mixin
* sets font related properties in a consistent way
* this is the only thing that gets used outside of this file
*****************************************************************************/
font($weight = normal, $style = normal) {
  
  // Decide which font-family to use
  if ($weight == bold) {
    if ($style == italic) {
      font-family: $fontFamilies.boldItalic, $fontGeneric;
    } else {
      font-family: $fontFamilies.bold, $fontGeneric;
    }
  } else {
    if ($style == italic) {
      font-family: $fontFamilies.italic, $fontGeneric;
    } else {
      font-family: $fontFamilies.regular, $fontGeneric;
    }
  }
        
  // the fonts already have the appropriate weight and style
  // so these should always be normal to prevent double bolding
  font-weight: normal;
  font-style: normal;
  letter-spacing: normal;
}

/* Create the @font-face declarations for each weight/style of font
* do not use these font-families manually, use the font() mixin instead
*****************************************************************************/
for $i, $fontFamily in $fontFamilies {
  // http://css-tricks.com/snippets/css/using-font-face/
  @font-face {
    font-family: $fontFamily;
    src: url($fontFamily + '.eot');
    src: url($fontFamily + '.eot?#iefix') format('embedded-opentype'),
      url($fontFamily + '.woff') format('woff'),
      url($fontFamily + '.ttf') format('truetype');
  }
}