[racket] Use of map and eval to evaluate symbol in namespace

Thanks, Vincent. But a recipe is more than those simple definitions.
Actually, it would be something like:


MEDICATION DOSE UNITS ----------------- QUANTITY FORM

     INSTRUCTIONS FOR TAKING MEDICATION

In my previous Forth version, this was extremely easy to achieve, as
Forth is syntax-less, and "code is data, and data is code". So the
recipe turned out to be a mini language written in Forth itself.

These seems to be harder in Scheme... Some here seem to shun code/data
 ("don't use eval") in favor of what would amount ultimately to
string-based methods, as far as I understand it.

- Henry





On Mon, Jul 28, 2014 at 6:03 PM, Vincent St-Amour <stamourv at ccs.neu.edu> wrote:
> Henry,
>
> It looks like modules may be what you're looking for.
>
> You could have a file that defines a substance and exports it
>
>     ;; a.rkt
>     #lang racket
>     (provide hctz25)
>     (define hctz25 "Hydrochlorothiazide 25mg")
>
> and then a recipe file that imports the previous file
>
>     #lang racket
>     (require "a.rkt")
>     hctz25
>
> The module system is the preferred way to share definitions across
> multiple files in Racket.
>
> Would that solve your problem?
>
> Vincent
>
>
> At Mon, 28 Jul 2014 17:21:40 -0300,
> Henry Lenzi wrote:
>>
>> Hi Neil --
>>
>> So how do you export hash keys as symbols to a file that can be read
>> in again, not as string?
>>
>> Now, I haven't gotten around to reading the whole of Racket Scheme's
>> documentation... Things are looking kind of hard.
>>
>> What I'm attempting to do is then read back the symbols defined, such
>> as the one below:
>>
>> (define hctz25 "Hydrochlorothiazide 25mg")
>>
>> > (close-input-port in)
>> > (define in (open-input-file "Recipe.txt"))
>> > (string->symbol (read-line in))
>> '|'hctz25|
>>
>> But what I really want is the "hctz25" symbol that evaluates to a
>> string. If I don't use string->symbol, I get the string "hctz25". And
>> why the bars ("|")? I've read
>>
>>  http://docs.racket-lang.org/reference/reader.html#%28part._parse-hashtable%29
>>
>> but it didn't help me much.
>>
>> Of course, the ultimate purpose would be to re-evaluate the imported
>> symbol and reconstruct a medical recipe. The purpose of these
>> baby-steps exercises is porting a medical recipe program I've written
>> originally in Forth that allowed me to service 5.000 patients creating
>> a little database of shorthand recipes that then expand into real
>> medical recipes. I got hundreds of patients on renewable recipes for,
>> say, hypertension. Hand writing is no fun. Typing them in Word is no
>> fun. The hospital has is its own software, but it's is a load of
>> baloney, extremely buggy, if you ask me, so I'm rolling my own again,
>> except I want to print directly on the model paper our service uses,
>> so I want graphics like Racket Scheme has (very good capabilities, as
>> far as my needs are concerned).
>>
>> With Forth, it's very easy to design DSLs, because there's no syntax
>> and you get a lot of advanced features for free. For instance, there's
>> no need to write a parser for my little language. However, since Forth
>> implementations fall short of dealing with images, graphics (unless
>> you take the royal road to pain and learn to program for the Win32 API
>> and how it works for a particular Forth vendor), I'm looking at Racket
>> Scheme.
>>
>> TIA,
>>
>> Henry Lenzi
>>
>>
>>
>>
>>
>>
>>
>>
>> On Mon, Jul 28, 2014 at 4:46 PM, Neil Van Dyke <neil at neilvandyke.org> wrote:
>> > I don't know the current state of the "eval" docs in the manual, but I think
>> > they should have a big warning at the very front, intended to scare away
>> > newbies.
>> >
>> > Remember that Racket is often used in conjunction with many different
>> > Scheme-based and other Lisp-based textbooks and courses. It seems that many
>> > CS instructors and textbook authors like to talk about ``EVAL'' (as an
>> > abstract operation) when talking about some models of evaluation, and "eval"
>> > (as an accessible language binding) to say, gosh, aren't dynamic languages
>> > interesting and powerful. So, we can't blame every fourth newbie for trying
>> > to use "eval" unnecessarily, in ways that make for bad software engineering.
>> >
>> > Given this reality of confusing instruction, I'm thinking that, as a
>> > reactive measure, "#lang paddle" will disable "eval" by default. Attempting
>> > to use "eval" will give you an error message, unless you have an assertion
>> > form like
>> > "(i-have-read-the-foo-document-and-understand-that-eval-is-usually-the-wrong-thing-but-honest-i-know-what-i-am-doing)".
>> >
>> > Cheers,
>> > Neil V.
>> >
>> > Vincent St-Amour wrote at 07/28/2014 02:21 PM:
>> >
>> >> Maybe this should be linked to from the `eval' docs?
>> >>
>> >>
>> >> http://blog.racket-lang.org/2011/10/on-eval-in-dynamic-languages-generally.html
>> >>
>> >> Vincent
>> >>
>> >>
>> >> At Sun, 27 Jul 2014 16:16:52 -0400,
>> >> Neil Van Dyke wrote:
>> >>>
>> >>> Maybe there should be a periodic public service announcement about not
>> >>> using "eval".  This time I will communicate in FAQ format:
>> >>>
>> >>> Q: How do I use eval?
>> >>> A: Don't use eval.
>> >>>
>> >>> Q: But don't so many academic books feature eval prominently, so doesn't
>> >>> that mean I should use try to eval?
>> >>> A: Those books use eval for pedagogic reasons, or because the author is
>> >>> enamored of some theoretical appeal of eval, or because the author wants
>> >>> to watch the world burn.  Don't use eval.
>> >>>
>> >>> Q: But, but, but, I am just starting to learn, and eval seems to do what
>> >>> I need.
>> >>> A: Eval is almost certainly not what you want.  Learn how to use the
>> >>> other basics effectively.  Don't use eval.
>> >>>
>> >>> Q: I now am very comfortable with the language, I am aware that I should
>> >>> avoid eval in almost all cases, and I can tell you why eval is actually
>> >>> the right thing in this highly unusual case.
>> >>> A: Cool, that's why eval is there.
>> >>>
>> >>> Neil V.
>> >>>
>> >
>> > ____________________
>> >  Racket Users list:
>> >  http://lists.racket-lang.org/users
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users