Vertical Rhythm module from Compass ported to Stylus

vertical-rhythm.styl

// Vertical Rhythm ported from SASS/Compass
// Works exactly as before, with four exceptions:
// 1. rhythm() is a mixin, $rhythm() is a function. Stylus doesn't differentiate between same-name mixins and functions
// 2. All of the variables you're used to lack the dollar sign ($) prepend.
// 3. debug-vertical-alignment uses a temporary online image solution via http://basehold.it
// 4. There is no h-borders alias. Use horizonatal-borders instead.

// The base font size.
base-font-size ?= 16px

// The base line height determines the basic unit of vertical rhythm.
base-line-height ?= 24px

// Set the default border style for rhythm borders.
default-rhythm-border-style ?= solid

// The default font size in all browsers.
browser-default-font-size = 16px

// Set to false if you want to use absolute pixels in sizing your typography.
relative-font-sizing ?= true

// Allows the `adjust-font-size-to` mixin and the `lines-for-font-size` function
// to round the line height to the nearest half line height instead of the
// nearest integral line height to avoid large spacing between lines.
round-to-nearest-half-line ?= false

// Ensure there is at least this many pixels
// of vertical padding above and below the text.
min-line-padding ?= 2px

// $base-font-size but in your output unit of choice.
// Defaults to 1em when `$relative-font-sizing` is true.
font-unit ?= relative-font-sizing ? 1em : base-font-size

// The basic unit of font rhythm.
base-rhythm-unit = font-unit * base-line-height / base-font-size

// The leader is the amount of whitespace in a line.
// It might be useful in your calculations.
base-leader = font-unit / base-font-size * (base-line-height - base-font-size)

// The half-leader is the amount of whitespace above and below a line.
// It might be useful in your calculations.
base-half-leader = base-leader / 2

// unitless() function borrowed from SASS
// TODO: move this to a utilities file
unitless(number)
  unit(number) is ''

// Function.
// True if a number has a relative unit.
relative-unit(number)
  unit(number) is '%' or unit(number) is 'em' or unit(number) is 'rem'

// Function.
// True if a number has an absolute unit.
absolute-unit(number)
  not (relative-unit(number) or unitless(number))

if (relative-font-sizing) and (not relative-unit(font-unit))
  warn('relative-font-sizing is true but font-unit is set to ' + font-unit + ' which is not a relative unit.')

// Mixin
// Establishes a font baseline for the given font-size.
establish-baseline(font-size = base-font-size)
  // IE 6 refuses to resize fonts set in pixels and it weirdly resizes fonts
  // whose root is set in ems. So we set the root font size in percentages of
  // the default font size.
  * html
    font-size 100% * (font-size / browser-default-font-size)
  html
    font-size font-size
    adjust-leading-to 1, relative-font-sizing ? font-size : base-font-size

// Show a background image that can be used to debug your alignments.
// Requires internet connection
// TODO: Make a better version of this
debug-vertical-alignment()
  background-image url('http://basehold.it/i/' + unit(base-line-height, ''))

// Adjust a block to have a different font size and line height to maintain the
// rhythm. $lines specifies how many multiples of the baseline rhythm each line
// of this font should use up. It does not have to be an integer, but it
// defaults to the smallest integer that is large enough to fit the font.
// Use $from-size to adjust from a font-size other than the base font-size.
adjust-font-size-to(to-size, lines = lines-for-font-size(to-size), from-size = base-font-size)
  if (not relative-font-sizing) and (from-size is not base-font-size)
    warn('relative-font-sizing is false but a relative font size was passed to adjust-font-size-to')
  font-size font-unit * (to-size / from-size)
  adjust-leading-to lines, relative-font-sizing ? to-size : base-font-size

// Adjust a block to have different line height to maintain the rhythm.
// $lines specifies how many multiples of the baseline rhythm each line of this
// font should use up. It does not have to be an integer, but it defaults to the
// smallest integer that is large enough to fit the font.
adjust-leading-to(lines, font-size = base-font-size)
  line-height $rhythm(lines, font-size)

// Calculate rhythm units.
$rhythm(lines = 1, font-size = base-font-size, offset = 0)
  if (not relative-font-sizing) and (font-size is not base-font-size)
    warn('relative-font-sizing is false but a relative font size was passed to the rhythm function')
  rhythm = font-unit * (lines * base-line-height - offset) / font-size
  // Round the pixels down to nearest integer.
  if unit(rhythm) is 'px'
    rhythm = floor(rhythm)
  return rhythm

// Calculate the minimum multiple of rhythm units needed to contain the font-size.
lines-for-font-size(font-size)
  lines = round-to-nearest-half-line ? ceil(2 * font-size / base-line-height) / 2 : ceil(font-size / base-line-height)
  if lines * base-line-height - font-size < min-line-padding * 2
    lines = lines + (round-to-nearest-half-line ? 0.5 : 1)
  return unit(lines, '')

// Apply leading whitespace. The $property can be margin or padding.
leader(lines = 1, font-size = base-font-size, property = margin)
  {property}-top $rhythm(lines, font-size)

// Apply leading whitespace as padding.
padding-leader(lines = 1, font-size = base-font-size)
  padding-top $rhythm(lines, font-size)

// Apply leading whitespace as margin.
margin-leader(lines = 1, font-size = base-font-size)
  margin-top $rhythm(lines, font-size)

// Apply trailing whitespace. The $property can be margin or padding.
trailer(lines = 1, font-size = base-font-size, property = margin)
  {property}-bottom $rhythm(lines, font-size)

// Apply trailing whitespace as padding.
padding-trailer(lines = 1, font-size = base-font-size)
  padding-bottom $rhythm(lines, font-size)

// Apply trailing whitespace as margin.
margin-trailer(lines = 1, font-size = base-font-size)
  margin-bottom $rhythm(lines, font-size)

// Shorthand mixin to apply whitespace for top and bottom margins and padding.
rhythm(leader = 0, padding-leader = 0, padding-trailer = 0, trailer = 0, font-size = base-font-size)
  leader leader, font-size
  padding-leader padding-leader, font-size
  padding-trailer padding-trailer, font-size
  trailer trailer, font-size

// Apply a border and whitespace to any side without destroying the vertical
// rhythm. The whitespace must be greater than the width of the border.
apply-side-rhythm-border(side, width = 1px, lines = 1, font-size = base-font-size, border-style = default-rhythm-border-style)
  if (not relative-font-sizing) and (font-size is not base-font-size)
    warn('relative-font-sizing is false but a relative font size was passed to apply-side-rhythm-border')
  border-{side}-style border-style
  border-{side}-width font-unit * (width / font-size)
  padding-{side} $rhythm(lines, font-size, offset = width)

// Apply borders and whitespace equally to all sides.
rhythm-borders(width = 1px, lines = 1, font-size = base-font-size, border-style = default-rhythm-border-style)
  if (not relative-font-sizing) and (font-size is not base-font-size)
    warn('relative-font-sizing is false but a relative font size was passed to rhythm-borders')
  border-style border-style
  border-width font-unit * (width / font-size)
  padding $rhythm(lines, font-size, offset = width)

// Apply a leading border.
leading-border(width = 1px, lines = 1, font-size = base-font-size, border-style = default-rhythm-border-style)
  apply-side-rhythm-border top, width, lines, font-size, border-style

// Apply a trailing border.
trailing-border(width = 1px, lines = 1, font-size = base-font-size, border-style = default-rhythm-border-style)
  apply-side-rhythm-border bottom, width, lines, font-size, border-style

// Apply both leading and trailing borders.
horizontal-borders(width = 1px, lines = 1, font-size = base-font-size, border-style = default-rhythm-border-style)
  leading-border width, lines, font-size, border-style
  trailing-border width, lines, font-size, border-style

Hello @declandewet, good job.
I edited a few things to use, look here.
What do you think of creating a bower package?