[racket] Dynamic Require of Syntax

From: Tim Brown (mightyfoo at gmail.com)
Date: Fri Feb 1 09:39:15 EST 2013

On 01/02/13 13:13, Matthias Felleisen wrote:
> Actually what does it mean to access syntactic extensions at run-time?

Just a thought, but is there a case for pulling the syntaxes into a
"run-time" test suite ("raco test", or even the GUI tester?) and testing
them there... e.g. do they transform a list of datums or a string of code
into an expected output of datums? Equally interesting, given an invalid
form (as a list of datums), to the macros fail, but without busting the
test environment because there has been a syntax error.

In a previous discussion(*), I have seen "positive" tests for macros...
I input a form and when run, the output displays the runtime-evaluated
result of the transformed macro.

Say we have:
(module+ test (require rackunit))
   (define/test (f x ...) (#:tests t ...) e ...)
     (module+ test
       t ...)
     (define (f x ...) e ...)))
(define/test (add-two a) (#:tests (check-= (add-two 2) 4 0)) (+ 2 a))
(define/test (add-three a) (#:tests (check-= (add-three 2) 5 0)) (+ 2 a))

I get no test results (i.e. success) for add-two. I get a test fails for
add-three. But if I now want to ensure/document (via a test) that the
following is an invalid syntax (all define/test forms should have a
#:tests form:

(define/test (add-four a) (check-= (add-four 2) 6 0) (+ 4 a))

This won't compile; I can't get off the starting line.

I have an outstanding question about "unit-testing" syntactic extensions
from a couple of weeks ago. What do the heavier users of syntaxes use to
unit test their macros?


* http://lists.racket-lang.org/users/archive/2013-January/055983.html

> On Feb 1, 2013, at 2:57 AM, Dan Grossman wrote:
>> Cody and I would love an answer to this question from 1.5 months ago if
>> anybody can point us in the right direction and/or ask us to clarify the
>> question.  Or if the answer is "that is not possible" then we'll do
>> something else.
>> Much thanks!
>> --Dan
>> On Mon, Dec 17, 2012 at 9:20 PM, Cody Schroeder <codeblack08 at gmail.com
>> <mailto:codeblack08 at gmail.com>> wrote:
>>       I'm in a position that I would like to use dynamic-require
>>     <http://docs.racket-lang.org/reference/Module_Names_and_Loading.html#(def._((quote._~23~25kernel)._dynamic-require))> to
>>     gain access to all of the provides in a module.  This is quite
>>     straightforward for normal procedures, but I also want this to
>>     include syntax.  However, I get this error when trying to dynamically
>>     require the blah macro from my test module:
>>     (dynamic-require "test.rkt" 'blah)
>>     blah: use does not match pattern: (blah body) in: blah
>>       From the spec, it says that "If the module exports provided as
>>     syntax, then a use of the binding is expanded and evaluated in a
>>     fresh namespace to which the module is attached" when using
>>     dynamic-require.  I don't understand how it's being used, though.
>>       Is there a way to use dynamic-require how I want?  Is there a
>>     better way?
>>     Cody

Posted on the users mailing list.