001 (ns walkmap.vertex
002 "Essentially the specification for things we shall consider to be vertices.")
003
004 (defn vertex?
005 "True if `o` satisfies the conditions for a vertex. That is, essentially,
006 that it must rerpresent a two- or three- dimensional vector. A vertex is
007 shall be a map having at least the keys `:x` and `:y`, where the value of
008 those keys is a number. If the key `:z` is also present, its value must also
009 be a number.
010
011 The name `vector?` was not used as that would clash with a function of that
012 name in `clojure.core` whose semantics are entirely different."
013 [o]
014 (and
015 (map? o)
016 (number? (:x o))
017 (number? (:y o))
018 (or (nil? (:z o)) (number? (:z o)))))
019
020 (def ensure3d
021 "Given a vertex `o`, if `o` has a `:z` value, just return `o`; otherwise
022 return a vertex like `o` but having thie `dflt` value as the value of its
023 `:z` key, or zero as the value of its `:z` key if `dflt` is not specified.
024
025 If `o` is not a vertex, throws an exception."
026 (memoize
027 (fn
028 ([o]
029 (ensure3d o 0.0))
030 ([o dflt]
031 (cond
032 (not (vertex? o)) (throw (Exception. "Not a vertex!"))
033 (:z o) o
034 :else (assoc o :z dflt))))))
035
036 (def ensure2d
037 "If `o` is a vertex, set its `:z` value to zero; else throw an exception."
038 (memoize
039 (fn [o]
040 (if
041 (vertex? o)
042 (assoc o :z 0.0)
043 (throw (Exception. "Not a vertex!"))))))