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LFE gen server Example

Revision as of 19:13, 10 January 2009 by Giara (Talk | contribs)


Lisp Flavored Erlang: gen_server Example

This is a very simple gen_server example. It implements a locally registered server which keeps an integer as state and can return the current integer or the next one (in which case the state will increment).

This example originally appeared on metajack's blog.


  • Save the code to count_server.lfe
  • Compile it from the Erlang shell with lfe_comp:file(count_server).

Using From the Erlang Shell

Since LFE modules are just like normal modules, you use them the same way:

  • Load the new module with l(count_server).
  • Start up the server with count_server:start_link().
  • Send it commands like count_server:current(). or count_server:next().

Using From the LFE Shell



;; count_server.lfe
;; Simple gen_server example. 

(defmodule count_server
  (behavior 'gen_server)

  ;; gen_server exports
   (init 1)
   (handle_call 3)
   (handle_cast 2)
   (handle_info 2)
   (terminate 2)
   (code_change 3))

  ;; public functions
   (start_link 0)
   (current 0)
   (next 0)))

;; gen_server implementation

(defun init (args)
  #(ok 0))

(defun handle_call 
  (('next _ n)
   (let ((new (+ n 1)))
     (tuple 'reply (tuple 'ok new) new)))
  (('current _ n)
   (tuple 'reply (tuple 'ok n) n))) 

(defun handle_cast (req state)
  (tuple 'stop #(error not_implemented) state))

(defun handle_info (info state)
  (tuple 'stop #(error not_implemented) state))

(defun terminate (reason state)

(defun code_change (oldvsn state extra)
  (tuple 'ok state))

;; public functions

(defun start_link ()
  (: gen_server start_link #(local count_server) 'count_server () ())) 

(defun current ()
  (: gen_server call 'count_server 'current))

(defun next ()
  (: gen_server call 'count_server 'next))