Nu functions

utilities.nu

#!/usr/local/bin/nush

;; @name utilities.nu
;; @description A set of utilities for Nu


(function ++ (num)
  (+ 1 num))
  
;; (puts (++ 15)) -> 16

(function last (some-list)
  (cdr some-list))

;; (puts (last '(1 2 3 4))) -> (2 3 4)

(function empty? (a-list)
  (eq 0 (a-list length)))
  
;; (puts (empty? '())) -> #t

(function number? (num)
  (eq (num class) NSCFNumber))
  
;; (number? 1) -> #t
  
(function odd? (num)
  (!= (% num 2) 0))

;; (odd? 5) -> #t
  
(function even? (num)
  (eq (% num 2) 0))

;; (even? 4) -> #t

(function member? (obj a-list)
  (eq ((a-list array) containsObject:obj) 1))

;; (member? 1 '(1 2 3 4)) -> t
  
(function cadr (a-list)
  (car (cdr a-list)))

;; (cadr '(beef pork chicken)) -> pork

(function select (predicate a-list)
  (cond ((empty? a-list) '())
        ((predicate (first a-list))
          (cons (first a-list) (select predicate (cdr a-list))))
        ((else (select predicate (cdr a-list))))))

;; (select number? '(1 3 chocolate 4 yogurt)) -> '(1 3 4)

(function accumulate (+ a-list)
  (if (empty? a-list)
    0
    (else
      (+ (first a-list) (accumulate + (cdr a-list))))))
        
;; (accumulate + '(1 2 3 4)) -> 10


;; Compose
;; Takes 2 arguments
;; Returns an anonymous function that takes one argument
(function compose (f g)
  (do (x) (f (g x))))
  
;; ((compose number? (do (x) (* x 4))) 3) -> #t
  
(function flatten (x)
  (set rec (do (x acc)
            (puts x)
            (cond ((nil x) nil)
                  ((atom x) (cons x acc))
                  ((else 
                    (rec (car x) (rec (cdr x) acc)))))))
  (rec x nil))
  
;; (flatten '((1 2 3) (4 5 6) ('seven 'eight '(nine)))) -> (1 2 3 4 5 6 seven eight nine)

6 December 2010: Updated select function. Add flatten function, but doesn't quite work as expected.