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• What is the syntax for tags?
  • Keywords, like #:tag form
    • One character longer
    • Slightly easier to parse
  • Symbols, like #tag form
    • One character shorter
    • Slightly harder to parse
    • Ambiguous with record constructors?
      • Not if we assume that: 
        • 1) record names always contain a dot
          • Which they must, because deftypes occur in namespaces
        • 2) user-defined tags are always namespace-qualified
        • 3) built-in tags do not contain a dot
• What happens when the reader encounters a tag for which no function is defined?
  • Error?
  • Return form unchanged?
  • Return form with extra metadata?
    • Only possible if form supports metadata, ignore otherwise?

• How to associate tags with reader functions?
  • file containing mapping from tags to Vars
    • "magic" file name gets loaded before other files
    • doesn't load any code directly
    • If 2 JARs on classpath have a magic file, who wins?
  • map stored in dynamic var
    • thread-local binding for each source file
      • created in Compiler.load
    • can be set! within a source file
    • can be rebound when invoking the reader at runtime

References / See Also

• Clojure Instant Literal & Library