The classical introductory exercise. Just say "Hello, World!".
"Hello, World!" is the traditional first program for beginning programming in a new language or environment.
The objectives are simple:
If everything goes well, you will be ready to fetch your first real exercise.
Your solution may be a procedure that returns the desired string or a variable whose value is that string.
Suppose you're solving halting-problem:
(load "halting-problem.scm")at the prompt.
(test)from the REPL. At first this should result in failed tests.
You can see more information about failing test cases by passing
arguments to the procedure
To see the failing input call
(test 'input) and to see the input and output together call
(test 'input 'output).
This is an exercise to introduce users to using Exercism http://en.wikipedia.org/wiki/%22Hello,_world!%22_program
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
(define test-fields '(input output who)) (define (test-run-solution solution input) (if (procedure? solution) (apply solution input) solution)) (define (test-success description success-predicate procedure input output) (call/cc (lambda (k) (with-exception-handler (lambda (e) (k `(fail (description . ,description) (input . ,input) (output . ,output) (who . ,procedure)))) (lambda () (let ([result (test-run-solution procedure input)]) (unless (success-predicate result output) (error 'exercism-test "test fails" description input result output))) `(pass . ,description)))))) (define (test-error description procedure input) (call/cc (lambda (k) (with-exception-handler (lambda (e) (k `(pass . ,description))) (lambda () (test-run-solution procedure input) `(fail (description . ,description) (input . ,input) (output . error) (who . ,procedure))))))) (define (run-test-suite tests . query) (for-each (lambda (field) (unless (and (symbol? field) (memq field test-fields)) (error 'run-test-suite (format "~a not in ~a" field test-fields)))) query) (let-values ([(passes failures) (partition (lambda (result) (eq? 'pass (car result))) (map (lambda (test) (test)) tests))]) (cond [(null? failures) (format #t "~%Well done!~%~%") 'success] [else (format #t "~%Passed ~a/~a tests.~%~%The following test cases failed:~%~%" (length passes) (length tests)) (for-each (lambda (failure) (format #t "* ~a~%" (cond [(assoc 'description (cdr failure)) => cdr] [else (cdr failure)])) (for-each (lambda (field) (let ([info (assoc field (cdr failure))]) (format #t " - ~a: ~a~%" (car info) (cdr info)))) query)) failures) (newline) 'failure]))) (define (test . args) (apply run-test-suite (list (lambda () (test-success "Say Hi!" equal? hello-world '() "Hello, World!"))) args))
(import (rnrs (6))) (load "test.scm") (define hello-world "Hello, World!")
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.