parser.rb

require 'parslet'

class FooParser < Parslet::Parser
  rule(:space)  { match('\s').repeat(1) }
  rule(:space?) { space.maybe }

  rule(:dot)    { str('.') >> space? }
  rule(:colon)  { str(':') >> space? }
  rule(:comma)  { str(',') >> space? }
  rule(:comma?) { comma.maybe }

  rule(:word)  { match('\w').repeat(1) }
  rule(:key)   { word >> space? }
  rule(:value) { match('[^,.]').repeat }

  rule(:pair)  { key.as(:key) >> colon >> value.as(:value) >> comma? }
  rule(:pairs) { pair.repeat(1) >> dot }

  rule(:foos) { pairs.as(:pair).repeat }
  root(:foos)
end

EXAMPLE = 'First: thing, Is :first. How:do, we : even.'
p FooParser.new.parse(EXAMPLE)

Ooo, this looks pretty nice.