       throw new UserException "svgtiler: unrecognized extension in filename #{filename}"
 
 class Mapping extends Input
+  constructor: (data) ->
+    if data?
+      for own key, value of data
+        unless value instanceof Symbol
+          value = Symbol.parse key, value
+        @[key] = value
 
 class ASCIIMapping extends Mapping
   @parse: (data) ->
-    map = new @
+    map = {}
     for line in splitIntoLines data
       separator = whitespace.exec line
       continue unless separator?

path = require 'path'
fs = require 'fs'
csvParse = require 'csv-parse'
xmldom = require 'xmldom'
DOMParser = xmldom.DOMParser


extension_map =
  '.txt': ASCIIMapping
  '.js': JSMapping
  '.coffee': CoffeeMapping
  '.asc': ASCIIDrawing
  '.ssv': SSVDrawing
