nihilismus's solution to Hello World on the Scheme track

Instructions

Test suite

Solution

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:

Write a function that returns the string "Hello, World!".
Run the test suite and make sure that it succeeds.
Submit your solution and check it at the website.

If everything goes well, you will be ready to fetch your first real exercise.

Track Specific Notes

Your solution may be a procedure that returns the desired string or a variable whose value is that string.

Running and testing your solutions

From the command line

Simply type make chez if you're using ChezScheme or make guile if you're using GNU Guile. Sometimes the name for the scheme binary on your system will differ from the defaults. When this is the case, you'll need to tell make by running make chez chez=your-chez-binary or make guile guile=your-guile-binary.

From a REPL

Enter (load "test.scm") at the repl prompt.
Develop your solution in hello-world.scm reloading as you go.
Run (test) to check your solution.

Failed Test Cases

If some of the test cases fail, you should see the failing input and the expected output. The failing input is presented as a list because the tests call your solution by (apply hello-world input-list). To learn more about apply see The Scheme Programming Language -- Chapter 5

Source

This is an exercise to introduce users to using Exercism http://en.wikipedia.org/wiki/%22Hello,_world!%22_program

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

test.scm

(import (except (rnrs) current-output-port))

(define test-fields '(input output))

(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)
      (let ([out (open-output-string)])
        (with-exception-handler
          (lambda (e)
            (let ([result `(fail
                             (description . ,description)
                             (input . ,input)
                             (output . ,output)
                             (stdout . ,(get-output-string out)))])
              (close-output-port out)
              (k result)))
          (lambda ()
            (let ([result (parameterize ([current-output-port out])
                            (test-run-solution procedure input))])
              (unless (success-predicate result output)
                (error 'exercism-test
                  "test fails"
                  description
                  input
                  result
                  output)))
            (let ([result `(pass
                             (description . ,description)
                             (stdout . ,(get-output-string out)))])
              (close-output-port out)
              result)))))))

(define (test-error description procedure input)
  (call/cc
    (lambda (k)
      (let ([out (open-output-string)])
        (with-exception-handler
          (lambda (e)
            (let ([result `(pass
                             (description . ,description)
                             (stdout . ,(get-output-string out)))])
              (close-output-port out)
              (k result)))
          (lambda ()
            (parameterize ([current-output-port out])
              (test-run-solution procedure input))
            (let ([result `(fail
                             (description . ,description)
                             (input . ,input)
                             (output . error)
                             (stdout . ,(get-output-string out)))])
              (close-output-port out)
              result)))))))

(define (run-test-suite tests . query)
  (for-each
    (lambda (field)
      (unless (and (symbol? field) (memq field test-fields))
        (error 'run-test-suite
          (format #t "~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!~%~%")]
      [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))])
                 (display "  - ")
                 (write (car info))
                 (display ": ")
                 (write (cdr info))
                 (newline)))
             query))
         failures)
       (error 'test "incorrect solution")])))

(define (run-docker test-cases)
  (write (map (lambda (test) (test)) test-cases)))

(define hello-world)

(define test-cases
  (list
    (lambda ()
      (test-success "Say Hi!" equal? hello-world '()
        "Hello, World!"))))

(define (test . query)
  (apply run-test-suite test-cases query))

(let ([args (command-line)])
  (cond
    [(null? (cdr args))
     (load "hello-world.scm")
     (test 'input 'output)]
    [(string=? (cadr args) "--docker")
     (load "hello-world.scm")
     (run-docker test-cases)]
    [else (load (cadr args)) (test 'input 'output)]))

(import (rnrs))

(define (hello-world)
  "Hello, World!")

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nihilismus's solution

to Hello World in the Scheme Track