madlisp/mad/calc.mad

;;
;; Simple command line calculator which demonstrates the following concepts:
;; - command parser with arguments
;; - readline support with history
;; - main loop
;;
;; This is a barebones example for creating interactive command line scripts.
;; This script should be executed directly, not inside the repl.
;;

;; Define commands
(defn cmdAdd (args) (apply + args))
(defn cmdDiv (args) (apply / args))
(defn cmdMod (args) (apply % args))
(defn cmdMul (args) (apply * args))
(defn cmdSub (args) (apply - args))
(defn cmdHelp () (str "Available commands: " (apply join ", " (keys cmdMap))))
(defn cmdQuit () (exit))

;; And we define a hash-map for command lookups with minimum number of arguments
(def cmdMap {
  "add": [cmdAdd 2]
  "div": [cmdDiv 2]
  "mod": [cmdMod 2]
  "mul": [cmdMul 2]
  "sub": [cmdSub 2]
  "help": [cmdHelp 0]
  "quit": [cmdQuit 0]
})

;; Find the first command which starts with the given name, or null
(defn findCmd (name)
  (if (empty? name) null
    (let (matches (filterh (fn (v k) (prefix? k name)) cmdMap))
      (if (empty? matches) null
        (get matches (first (keys matches)))))))

;; Split input by spaces, find command that matches the first word
;; and call it, giving the rest of the words as arguments.
(defn parseInput (inp)
  (let (words (split " " inp) cname (first words) args (tail words) cmd (findCmd cname))
    (if (null? cmd) "Unknown command, try 'help'."
      (if (< (len args) (second cmd)) (str "Give at least 2 arguments to " cname ".")
        ((first cmd) args)))))

;; Define a file for readline and load it
(def readlineFile (str HOME "calc_history"))
(readline-load readlineFile)

;; Main loop: Read input from user, add it to readline, and parse it
(while true
  (let (inp (readline "[calc] "))
    (readline-add inp)
    (readline-save readlineFile)
    (print "⇒ " (parseInput inp) EOL)))