Hash table

my-hash-table.lisp

(defpackage #:my-hash-table
  (:use #:cl #:arrows)
  (:export #:new-hash #:put-hash #:get-hash #:hash-keys #:hash-values #:rem-hash))

(in-package #:my-hash-table)

(defun ->hash-code (key)
  (-<> (format nil "~A" key)
       (coerce <> 'list)
       (reduce (lambda (hash elem) (+ (* 31 hash) (char-code elem))) <> :initial-value 0)))

(defun ->position (table-size key)
  (rem (->hash-code key) table-size))

(defun new-hash (&optional (size 100))
  (make-array (list size) :initial-element nil))

(defun get-hash (table key &optional default)
  (let ((pos (->position (length table) key)))
    (-<> (aref table pos)
	 (assoc key <> :test #'eq)
	 (cdr)
	 (or <> default))))

(defun put-hash (table key item)
  (let* ((pos (->position (length table) key))
	 (chain (aref table pos))
	 (pair (assoc key chain :test #'eq)))
    (prog1
	(cdr pair)
        (if (null pair)
	  (push (cons key item) (aref table pos))
	  (rplacd pair item)))))

(defun hash-size (table)
  (-<>> (coerce table 'list)
	(mapcar #'length)
	(reduce #'+ <> :initial-value 0)))

(defun rem-hash (table key)
  (let* ((pos (->position (length table) key))
	 (chain (aref table pos)))
    (delete-if (lambda (x) (eq key (car x))) chain)))

(defun collect (table fn)
  (->> (coerce table 'list)
       (mapcar (lambda (xs) (mapcar fn xs)))
       (apply #'append)))

(defun hash-keys (table)
  (collect table #'car))

(defun hash-values (table)
  (collect table #'cdr))