2-fer is short for two for one. One for you and one for me.
Given a name, return a string with the message:
One for X, one for me.
Where X is the given name.
However, if the name is missing, return the string:
One for you, one for me.
Here are some examples:
|Name||String to return|
|Alice||One for Alice, one for me.|
|Bob||One for Bob, one for me.|
|One for you, one for me.|
|Zaphod||One for Zaphod, one for me.|
While Common Lisp doesn't care about indentation and layout of code, nor whether you use spaces or tabs, this is an important consideration for submissions to exercism.io. Excercism.io's code widget cannot handle mixing of tab and space characters well so using only spaces is recommended to make the code more readable to the human reviewers. Please review your editors settings on how to accomplish this. Below are instructions for popular editors for Common Lisp.
Use the following commands to ensure VIM uses only spaces for indentation:
:set tabstop=2 :set shiftwidth=2 :set expandtab
(or as a oneliner
:set tabstop=2 shiftwidth=2 expandtab). This can
be added to your
~/.vimrc file to use it all the time.
Emacs is very well suited for editing Common Lisp and has many powerful add-on packages available. The only thing that one needs to do with a stock emacs to make it work well with exercism.io is to evaluate the following code:
(setq-default indent-tabs-mode nil)
This can be placed in your
order to have it set whenever Emacs is launched.
One suggested add-on for Emacs and Common Lisp is SLIME which offers tight integration with the REPL; making iterative coding and testing very easy.
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
;;; ;;; two-fer v1.2.0 ;;; (ql:quickload "lisp-unit") #-xlisp-test (load "two-fer") (defpackage #:two-fer-test (:use #:common-lisp #:lisp-unit)) (in-package #:two-fer-test) (define-test no-name-given-nil (assert-equal "One for you, one for me." (two-fer:twofer nil))) (define-test a-name-given (assert-equal "One for Alice, one for me." (two-fer:twofer "Alice"))) (define-test another-name-given (assert-equal "One for Bob, one for me." (two-fer:twofer "Bob"))) (define-test no-name-given (assert-equal "One for you, one for me." (two-fer:twofer))) #-xlisp-test (let ((*print-errors* t) (*print-failures* t)) (run-tests :all))
(in-package #:cl-user) (defpackage #:two-fer (:use #:cl) (:export #:twofer)) (in-package #:two-fer) (defun twofer (&optional name) (format nil "One for ~A, one for me." (if name name "you")))
Mentor pointed out more idiomatic way of writing the `if` form: `(or name "you")`