LISP Cannot take CAR of T -


i trying evaluate each atom of list , see if it's equal number provided , remove if not running slight problem.

i wrote following code:

(defun equal1(v l)      (cond((= (length l) 0))           (t (cond( (not(= v (car(equal1 v (cdr l))))) (cdr l) )))      ) )  (equal1 5 '(1 2 3 4 5))

i obtain following error

error: cannot take car of t.

if add (write "hello") action if true, following error obtained:

error: cannot take car of "hello".

i'm still quite new lisp , wondering going on , how fix evaluate each atom , remove if not, cdr l action.

there couple of things improve function.

firstly, let's indent 

(defun equal1 (v l)   (cond     ((= (length l) 0))     (t (cond          ((not (= v (car (equal1 v (cdr l))))) (cdr l))))))

rather saying (= (length l) 0), can use (zerop (length l)). minor sylistic point. worse branch returns no value. if list l empty should return?

the issue function in t branch of first cond.

what want is

  1. remove list item same value v
  2. keep item not = v

the function should return list.

the expression

(cond    ((not (= v (car (equal1 v (cdr l))))) (cdr l)))

is trying (i think) deal both conditions 1 , 2. it's not working.

we have recall items in list , result of equal function needs list. in expression above result of function boolean , hence result of function call boolean.

the function needs step along each element of list , when sees matching value, skip it, otherwise use cons function build filtered output list.

here skeleton out. notice don't need embedded cond , have 3 conditions deal - list empty, filter value out, or continue build list.

(defun equal-2 (v l)   (cond     ((zerop (length l))  nil)     ((= v (car l))  <something goes here>)      ;skip or filter value     (t (cons (car l) <something goes here>)))) ;build output list

of course, being common lisp, there built-in function this. can remove-if...


Comments

Post a Comment

Popular posts from this blog

angular - Ionic slides - dynamically add slides before and after -

hi i'm using ngfor create set of 3 slides while starting in middle i'm guaranteed able slide left or right on start. when slide right can simple listen reachedend , push slide array i'm looping. but have problem adding slide beginning. if same above , use e.g. array.unshift() or spread add item beginning, view think it's on position 0 , snaps view new slide. the code below work animates slide change index 1. slide = [0,1,2] //example loop slidechanged(event) { if(this.slides.isbeginning()){ this.slide = [this.slide[0]-1, ...this.slide]; this.slides.update(); this.slides.slideto(1) } } <ion-slides [initialslide]="1" (ionslidedidchange)="slidechanged($event)"> <ion-slide *ngfor="let item of slide"> <h1>slide {{item}}</h1> </ion-slide> </ion-slides> any appreciated! you can using ionslidenextend , ionslideprevend events slides . please
Read more

minify - Minimizing css files -

i want know how css files can minimized. currently, using external sites css minifier compress css files. however, after removing whitespaces, comments, etc, file sizes reduced 10-15%. how frameworks bootstrap manage make minimized versions kilobytes. as example, css is: body { background-color: #ff0; } the reduction goes 28 bytes 22 bytes other css files have lot more characters still smaller this. actually minifying code means it's remove thing code white space characters new line characters comments block delimiters it reduces amount of code has transferred on web , speed site load fastly.but unreadable format.
Read more

Add a dynamic header in angular 2 http provider -

i have http interceptor built via tutorial https://scotch.io/@kashyapmukkamala/using-http-interceptor-with-angular2 the problem need have dynamic header changes automatically once changes 'mode' in app. service able tell interceptor change header, or have interceptor pull header (which string)from service each request. able throwing away patch method, call http.patch('new header string') set header string. call in service controls 'mode' setting. wondering if there way interceptor pull recent value service each request or if can add method http provider via interceptor? i've tried call service in interceptor each request returns undefined. because creating new instance of service or copying value before service fired , loaded/changed data. i don't want pass header string every http provider call because defeats purpose of having interceptor, id able set once changes or have provider fetch service before makes request. tl;dr : need add autom
Read more