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A syntax-rules macro expanding into left-leaning red-black tree code. Pure and mutating versions.


A left-leaning red–black (LLRB) tree is a type of self-balancing binary search tree. It is a variant of the red–black tree and guarantees the same asymptotic complexity for operations. [wikipedia].

The macro is independent of data structures used to implement nodes of the trees. Users must pass accessors and a syntax or procedure to update an existing node (for the mutating version) respectively create a fresh node as well as names for the procedures to be defined.


See the llrb-tree egg.



   init-root-node!		;; defined
   t-lookup		;; defined
   t-min			;; defined
   t-fold			;; defined
   t-for-each		;; defined
   t-insert		;; defined
   t-delete		;; defined
   t-delete-min		;; defined
   t-empty?		;; defined
   ;; These syntax is used expand to code for comparision
   ;; expressions.
   t-k-eq?			;; key<>node-key "equal"
   t-eq?			;; node-key<>node-key "equal"
   t-k-<?			;; key<>node-key "less then"
   t-<?			;; node<>node "less then"
   ;; Accessors to the elements of the tree.


FEATURES: {ordered, pure, leftmost} – configures the generated code.


The "update*" syntax must accept a node structure and key-value pairs. Keys are color:, left: and right:

"update" : If feature "pure" is set, "update" must expand to a newly allocated node, otherwise is MUST expand to a side effect full update of the original node.