Re: Land of lisp to Clojure

[Cecil Westerhof]

2014-07-09 2:24 GMT+02:00 Bruce Wang :

> You might want to check out this
> https://github.com/quux00/land-of-lisp-in-clojure
>

​I will look into it. But I learn most if I do it myself. ;-)​


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Re: Land of lisp to Clojure

[Cecil Westerhof]

2014-07-09 5:11 GMT+02:00 Timothy Baldridge :

> Prefer vectors over quoted lists '(1 2) vs [1 2]. There's rarely a case
> (outside of macros) that you want the former.
>
> Instead of quoted lists of symbols: '(You cannot get that.) try strings
> "You cannot get that"
>

​That is what Conrad uses. I would think that strings are much better also,
but he says that there is a good reason to use a quoted list of symbols.
And I have not finished the book yet. So maybe he is right.

​


> Don't use defs inside defs. Instead move the defs to a global position and
> then use binding or set-var-root! to set them.
>

​I was not happy with it, but did not know better. At the moment I get
binding and set-var-root! not working.

​


> Better yet, use atoms to hold their contents, even better yet, pass the
> game state into each function and have each function return a new game
> state.
>
> Instead of:
>
> (defn walk [direction]
>   ...
>   (def ^:dynamic *location* (first edge))
>
> Use atoms like this:
>
> (def location (atom nil))
>
> (defn walk [direction]
>   ...
>   (reset! location (first edge))
>

​Yep, that would be better. I al-ready use atom in error-in-datastruct-p,
so why not here?

​


> Once you replace symbol lists with strings, you can easily do this instead
> of syntax quoting:
>
> (str "There is a " (nth edge 2) " going " (nth edge 1) "from here")
>

​As said: that was my idea also. I just finish the book to see if there is
a real reason to use a quoted list. If not I replace it.



> On Tue, Jul 8, 2014 at 6:24 PM, Bruce Wang  wrote:
>
>> Hi Cecil,
>>
>> You might want to check out this
>> https://github.com/quux00/land-of-lisp-in-clojure
>>
>> Cheers,
>> Bruce
>>
>>
>> On Wed, Jul 9, 2014 at 9:49 AM, Cecil Westerhof 
>> wrote:
>>
>>> I received the book land of lisp as a gift. I am trying to translate it
>>> to Clojure. In chapter 5 there is a text game engine. In the attachment my
>>> translation. What do you think of it?
>>>
>>> There are a few problems.
>>> - The book displays all the lines of a look on separate lines. In my
>>> case it is just one long line. Am I doing something wrong?
>>>
>>> - In Emacs Lisp you can use a function A in the definition of another
>>> function B before you declared function A. Is it correct that this is not
>>> possible in Clojure?
>>>
>>> - Al variables in land of lisp begin and end with an asterisk. As I
>>> understood it, you only do this for variables that can be changed. So I
>>> renamed some variables. Did I understand this correctly, or is the usage of
>>> asterisks for something else?
>>>
>>
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Re: Land of lisp to Clojure

[Cecil Westerhof]

2014-07-09 5:30 GMT+02:00 John Mastro :

> Cecil Westerhof  wrote:
> > - The book displays all the lines of a look on separate lines. In my
> > case it is just one long line. Am I doing something wrong?
>
> No, you're not doing anything wrong. There's nothing in that data
> structure which would inherently cause it to print on multiple lines.
>
> If you're using Cider, you can enable automatic pretty-printing in the
> REPL, which would likely cause it to print on multiple lines. I think
> it's M-x cider-repl-toggle-pretty-printing.
>
> Or you could use a definition of look more like this, which uses println
> to print each item on its own line (not sure if you wanted to retain the
> parens or not, but both are easily doable).
>
> (defn look []
>   (doseq [d [(describe-location *location* nodes)
>  (describe-paths *location* edges)
>  (describe-objects *location* objects *object-locations*)]]
> (println d)))
>

​That certainly looks better. The only problem is that the lines of the
different calls are still printed as one. But rewriting to use strings
would solve that problem. I just have to finish the book, to see if I can
change the lists to strings.​



> - In Emacs Lisp you can use a function A in the definition of another
> > function B before you declared function A. Is it correct that this is
> > not possible in Clojure?
>
> Correct, though you can declare it without defining it, e.g.
> (declare function-a).
>

​OK, good to know.​




> > - Al variables in land of lisp begin and end with an asterisk. As I
> > understood it, you only do this for variables that can be changed. So
> > I renamed some variables. Did I understand this correctly, or is the
> > usage of asterisks for something else?
>
> The "earmuffs" convention is related to dynamic variables. All global
> variables are dynamic in Common Lisp, but that's not the case in
> Clojure. You're creating dynamic variables (by using :dynamic metadata
> in your defs) but I didn't notice anywhere where you're using this
> feature (i.e. no binding or set! forms). Long story short, I would use
> earmuffs if the variables are dynamic but not otherwise.
>

​I read a little about it. And no, I do not use dynamic binding. So I
probably should use atoms. Is there a convention how to name atoms?​




> Speaking of global variables, I'd recommend only using def at top level
> (it creates global vars regardless of where you use it). Perhaps it
> would work to initialize them at top level with a "null value", like
> (def something (atom nil)), and then set it later if/when appropriate,
> like (reset! something (first whatever)). As a plus, if you use
> atoms like this you most likely won't need dynamic variables, even if
> you need to start changing global variable values later on.
>

​Yep, I should do that.​




> Hope that helps,
>

​Certainly.

-- 
Cecil Westerho
​f​

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Re: Local variable

[Cecil Westerhof]

2014-07-09 4:19 GMT+02:00 Bob Hutchison :

>
> On Jul 8, 2014, at 7:08 PM, Cecil Westerhof 
> wrote:
>
> 2014-07-08 23:11 GMT+02:00 Bob Hutchison :
>
>>
>> On Jul 8, 2014, at 9:40 AM, Cecil Westerhof 
>> wrote:
>>
>> > In Clojure you can define a local constant with let, but I need a
>> variable (I think).
>> >
>> > I want to do the following. I have a function that checks several
>> things. Every time an error is found I want to set the variable errors to:
>> > (concat errors new-error)
>> >
>> > Is this possible? Or is there a better way to do this?
>>
>> Here's a different take on your question, and a few comments about how
>> I'd write that code. I don't think you need the atom -- kinda ugly and the
>> reduce/map/filter family of sequence functions will take you a long way.
>>
>> ; This is not a predicate, so don't use the -p suffix (and in Clojure
>> it's a ? normally)
>>
>
> ​As I understood it (I am rewriting land of lisp to Clojure) that when a
> function returns a true/false state, that you then use the -p suffix. When
> returning () there are no errors. But I should use the ? then?
>
>
> You’re returning a list of errors. You can interpret that as a
> truthy/falsy kind of thing, in which case make sure you’re returning a nil
> for the no-error case. And use the ‘?’ in Clojure.
>

​That I do with:
(let [errors (atom ())]

I changed the name to 'error-in-datastruct?'.


By the way. The current function is only the start of the checks.​
>
> ​After the if I need to do several other checks also. So I think I do need
> the atom. But maybe I am mistaken. ;-)
>
>
> I thought maybe your checks would be a little more than that. That’s why I
> left the ‘reduce’ version in there. Just make the function that is applied
> by reduce more powerful, perhaps pull it out into a separate function
> rather than an inline anonymous function. This will work as long as all
> tests are performed on one object at a time.
>
> No matter what, I’d recommend not going using an atom if you can help it.
>

​I have my work cut out. But that is the best way to learn. :-D

-- 
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Re: Land of lisp to Clojure

[Cecil Westerhof]

2014-07-09 9:39 GMT+02:00 Cecil Westerhof :

> Or you could use a definition of look more like this, which uses println
>
>> to print each item on its own line (not sure if you wanted to retain the
>> parens or not, but both are easily doable).
>>
>> (defn look []
>>   (doseq [d [(describe-location *location* nodes)
>>  (describe-paths *location* edges)
>>  (describe-objects *location* objects
>> *object-locations*)]]
>> (println d)))
>>
>
> ​That certainly looks better. The only problem is that the lines of the
> different calls are still printed as one. But rewriting to use strings
> would solve that problem. I just have to finish the book, to see if I can
> change the lists to strings.​
>
>

​Solved it without reverting to stings. See attachment. The only 'problem'
are the parentheses. How to get rid of those?

​


> > - Al variables in land of lisp begin and end with an asterisk. As I
>
>> > understood it, you only do this for variables that can be changed. So
>> > I renamed some variables. Did I understand this correctly, or is the
>> > usage of asterisks for something else?
>>
>> The "earmuffs" convention is related to dynamic variables. All global
>> variables are dynamic in Common Lisp, but that's not the case in
>> Clojure. You're creating dynamic variables (by using :dynamic metadata
>> in your defs) but I didn't notice anywhere where you're using this
>> feature (i.e. no binding or set! forms). Long story short, I would use
>> earmuffs if the variables are dynamic but not otherwise.
>>
>
> ​I read a little about it. And no, I do not use dynamic binding. So I
> probably should use atoms. Is there a convention how to name atoms?​
>

​Got also rid of the dynamic variables.

-- 
Cecil Westerhof

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land-of-lisp-text-game.clj
Description: Binary data

Re: [ANN] clojure-scheme - Compiling Clojure to Scheme to C

[Dry Jin]

By the way, how does Clojure-Scheme hand the Clojures's libraries over to 
Gambit-C?

2012년 3월 15일 목요일 오전 6시 8분 2초 UTC+9, Nathan Sorenson 님의 말:
>
> I've modified the output of the ClojureScript compiler to emit Scheme 
> code. At this point the core library is successfully compiled by Gambit 
> Scheme. A nice advantage of this is that Gambit compiles code via C, 
> meaning that stand-alone Clojure executables are now available for any 
> platform with a suitable gcc compiler!
>
> Gambit, notably, also compiles to iOS. Just recently I've confirmed that 
> Clojure's core library runs on the iPad simulator.
>
> There is a ton of yak-shaving required at this point---compilation 
> consists of a combination of shell commands, Clojure-interpreted commands 
> and Gambit-interpreted commands. Hopefully this will soon be streamlined.
>
> https://github.com/takeoutweight/clojure-scheme
>

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Re: Why clojure does not have pure lazy-evaluation like Haskell ?

[Colin Fleming]

True, but I think that's why he argues for a strict language which controls
side effects via monads, as Haskell does.


On 9 July 2014 07:18, Magnus Therning  wrote:

> On Tue, Jul 08, 2014 at 08:39:30PM +0200, Colin Fleming wrote:
> > I searched for this as well, and found this:
> > http://www.cs.nott.ac.uk/~gmh/appsem-slides/peytonjones.ppt
> >
> > "Purity is more important than, and quite independent of, laziness"
> >
> > and
> >
> > "The next ML will be pure, with effects only via monads.  The next
> Haskell
> > will be strict, but still pure."
>
> In the same presentation he also says that laziness has forced Haskell
> to stay pure, and that
>
> "Every call-by-value language has given into the siren call of side
> effects."
>
> So even if they are independent on the technical level one could say
> that they are dependent on a design/social level.
>
> /M
>
> --
> Magnus Therning  OpenPGP: 0xAB4DFBA4
> email: mag...@therning.org   jabber: mag...@therning.org
> twitter: magthe   http://therning.org/magnus
>
> Most software today is very much like an Egyptian pyramid with
> millions of bricks piled on top of each other, with no structural
> integrity, but just done by brute force and thousands of slaves.
>  -- Alan Kay
>

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How to use functions from clojure.contrib?

[Pierre Masci]

Hi, I am new to Clojure (about a week) so I might be missing something.

I want to use the (positions) 
 function 
from clojure.contrib.seq.
I could simply copy its source, but I would prefer a more generic way of 
using functions form clojure.contrib.
This page  indicates that 
clojure.contrib is deprecated, but I could not find (positions) anywhere 
else.

What is a good solution to this problem?

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Re: Client side tools for Clojure web app (back end questions as well, especially Pedestal)

[Jonathon McKitrick]

My new project is coming along nicely already.  I'm currently using XHR
calls to populate atoms on the client side, which are then automatically
rendered into the DOM via Reagent components.  It's wonderful, so far.


--
Jonathon McKitrick


On Tue, Jul 8, 2014 at 3:37 PM, Ahmad Hammad  wrote:

> Brendan, could you please elaborate on how you handled client/server
> communication with a project using Reagent/Om?
>
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Re: How to use functions from clojure.contrib?

[Andy Fingerhut]

Pierre:

The link to the page "Where did Clojure.Contrib Go" on the page where you
noted that clojure.contrib is deprecated gives the names of current
"modular" contrib libraries that contain most or all of what *some* older
clojure.contrib libraries contained.

Unfortunately clojure.contrib.seq has no corresponding current library
listed on that page, and I am not aware of any other place that
functionality may have been copied to.

CrossClj [1] might make it possible to find a more modern library where the
function positions was copied to that you could use (enter positions in the
search box at the upper right of the page).  However, I suspect that method
will quickly reach a point of diminishing returns if all you want is that
one function -- copying it into your code isn't a bad idea.

[1] http://crossclj.info

Andy



On Wed, Jul 9, 2014 at 4:20 AM, Pierre Masci  wrote:

> Hi, I am new to Clojure (about a week) so I might be missing something.
>
> I want to use the (positions)
>  
> function
> from clojure.contrib.seq.
> I could simply copy its source, but I would prefer a more generic way of
> using functions form clojure.contrib.
> This page  indicates that
> clojure.contrib is deprecated, but I could not find (positions) anywhere
> else.
>
> What is a good solution to this problem?
>
> --
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Re: Land of lisp to Clojure

[Cecil Westerhof]

2014-07-09 10:38 GMT+02:00 Cecil Westerhof :

> 2014-07-09 9:39 GMT+02:00 Cecil Westerhof :
>
> Or you could use a definition of look more like this, which uses println
>>
>>> to print each item on its own line (not sure if you wanted to retain the
>>> parens or not, but both are easily doable).
>>>
>>> (defn look []
>>>   (doseq [d [(describe-location *location* nodes)
>>>  (describe-paths *location* edges)
>>>  (describe-objects *location* objects
>>> *object-locations*)]]
>>> (println d)))
>>>
>>
>> ​That certainly looks better. The only problem is that the lines of the
>> different calls are still printed as one. But rewriting to use strings
>> would solve that problem. I just have to finish the book, to see if I can
>> change the lists to strings.​
>>
>>
>
> ​Solved it without reverting to stings. See attachment. The only 'problem'
> are the parentheses. How to get rid of those?
>

​Solved that one also:
(defn look []
  (doseq [d (concat (describe-location @location nodes)
(describe-paths@location edges)
(describe-objects  @location objects object-locations))]
(apply println d)))

-- 
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Re: How to use functions from clojure.contrib?

[Pierre Masci]

Thank you Andy, that's exactly the answer I needed.
I thought I might be missing "the right place where to look", because I'm 
new to the ecosystem.
http://crossclj.info 

 is 
a very good resource to know of.

I will copy-paste that function for now.

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Re: [ANN] Grimoire: up to date Clojure web docs

[Alex P]

There's also a version of what you wrote (at least something very similar), 
where one can specify libraries he wants docs for and have it all running 
either locally or on some webserver: https://github.com/ifesdjeen/gizmo-cloc
Adds code snippets with highlights and lucene-backed search.

On Wednesday, July 2, 2014 1:34:38 AM UTC+2, Reid McKenzie wrote:
>
> Hey guys, 
>
> If you're like me while using clojure.repl/doc works for the most part 
> there are just times that you need to send someone a link to the 
> official docs and navigating the docstrings in the core Clojure 
> repository is a pain. 
>
> After several months of being frustrated that clojuredocs is out of 
> date, I finally sat down and built an alternative which I'm pleased to 
> present here: http://www.arrdem.com/grimoire/ 
>
> Grimoire is still alpha and subject to change, especially with regards 
> to the example contribution process which needs streamlining beyond the 
> current "click a link, edit on github and submit a PR". 
>
> I'd like to give a shout out to César for porting clojure.repl/source 
> into the doc generation script and to Nicola for his random usability 
> criticisms. 
>
> Reid McKenzie 
>

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[ANN] Cats: category theory abstractions library for clojure(script).

[Andrey Antukh]

Hello everyone!

I just wanted to announce cats: category theory abstractions library for
clojure(script).

Why another library?
You can see a list of differences with existing libraries here:
http://niwibe.github.io/cats/#_why_another_library

Github: https://github.com/niwibe/cats
Documentation: http://niwibe.github.io/cats/

Best regards.
Andrey

-- 
Andrey Antukh - Андрей Антух -  / 
http://www.niwi.be 
https://github.com/niwibe

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Re: IllegalArgumentException when running core.async example

[endbegin]

Thanks!! That did it.

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How to access record in a hashmap

[Cecil Westerhof]

When you have:
(def object-locations {
 'whiskey   'living-room
 'bucket'living-room
 'chain 'garden
 'frog  'garden
 'dummy 'nowhere
 'test  'nowhere
 })

You can retrieve the location of the bucket with:
(object-locations 'bucket)
and with:
('bucket object-locations)

Personally I find the first better, but ‘Clojure Programming' uses the
second possibility. What is the better way and why?

-- 
Cecil Westerhof

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Re: Proposing a new Clojure documentation system (in Clojure)

[Edwin Watkeys]

On Tuesday, May 6, 2014 10:39:47 AM UTC-4, Gregg Reynolds wrote:
>
>
> On Tue, May 6, 2014 at 4:53 AM, Phillip Lord  > wrote:
>
Trivial things that I would like to be able to do that I cannot do (in a
>>
> way which will be reliably interpreted).
>>
>>  - Add hyperlinks
>>  - Distinguish between symbols (or names of vars) and normal words.
>>  - Distinguish between code (examples) and normal words
>>  - Have access to basic "markdown" style typography.
>>
>
> I'm undecided on these.  They would obviously be useful, but on the other 
> hand minimalism has its virtues.  In the base case of reading code with a 
> plaintext editor, I usually find embedded doco with lots of markup annoying 
> and an impediment to code reading.  I think I'm inclined to favor keeping 
> markup out of code but I'm keeping an open mind about it.
>

Gregg,

I strongly opposed the introduction of case-sensitive identifiers in R6RS 
Scheme. Case-insensitive identifiers allow programmers to write comments 
and documentation that unambiguously refer to arguments and function names 
in ALL-CAPS. As a bonus, a sentence need never begin with a capital letter, 
even if one is using something like back-ticks to indicate monospaced type, 
because `All-caps` is an equally valid representation. There are legitimate 
reasons to embrace case-sensitive identifiers, but the happy interplay 
between pre-R5RS source code and the written word was lost.

In Clojure doc strings, I either pretend that identifiers are 
case-insensitive or use back-ticks and try very hard not to start sentences 
with lower-case identifiers. Regarding code itself, I tend to use all-caps 
identifiers for macro arguments, another common Scheme (and Lisp?) 
convention, to make it more clear what's going on during quasi-quoting.

Edwin

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Re: How to access record in a hashmap

[Thomas Heller]

Short and simple answer: NullPointerException

(def object-locations nil)

(object-locations 'bucket) will throw
('bucket object-locations) => nil

HTH,
/thomas

On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>
> When you have:
> (def object-locations {
>  'whiskey   'living-room
>  'bucket'living-room
>  'chain 'garden
>  'frog  'garden
>  'dummy 'nowhere
>  'test  'nowhere
>  })
>
> You can retrieve the location of the bucket with:
> (object-locations 'bucket)
> and with:
> ('bucket object-locations)
>
> Personally I find the first better, but ‘Clojure Programming' uses the 
> second possibility. What is the better way and why?
>
> -- 
> Cecil Westerhof 
>

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Re: How to access record in a hashmap

[Thomas Heller]

Oh and its rare (outside of macros) to use symbols like that. Usually you'd
use keywords.

(def object-locations
  {:whiskey :living-room})


On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller  wrote:

> Short and simple answer: NullPointerException
>
> (def object-locations nil)
>
> (object-locations 'bucket) will throw
> ('bucket object-locations) => nil
>
> HTH,
> /thomas
>
> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>>
>> When you have:
>> (def object-locations {
>>  'whiskey   'living-room
>>  'bucket'living-room
>>  'chain 'garden
>>  'frog  'garden
>>  'dummy 'nowhere
>>  'test  'nowhere
>>  })
>>
>> You can retrieve the location of the bucket with:
>> (object-locations 'bucket)
>> and with:
>> ('bucket object-locations)
>>
>> Personally I find the first better, but ‘Clojure Programming' uses the
>> second possibility. What is the better way and why?
>>
>> --
>> Cecil Westerhof
>>
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Re: How to access record in a hashmap

[Cecil Westerhof]

2014-07-09 17:03 GMT+02:00 Thomas Heller :

> Short and simple answer: NullPointerException
>
> (def object-locations nil)
>
> (object-locations 'bucket) will throw
> ('bucket object-locations) => nil
>

​That is interesting.​

​Not a problem, because it will never be ​nil, but always a HashMap. But
better save as sorry. I will change it.



> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>>
>> When you have:
>> (def object-locations {
>>  'whiskey   'living-room
>>  'bucket'living-room
>>  'chain 'garden
>>  'frog  'garden
>>  'dummy 'nowhere
>>  'test  'nowhere
>>  })
>>
>> You can retrieve the location of the bucket with:
>> (object-locations 'bucket)
>> and with:
>> ('bucket object-locations)
>>
>> Personally I find the first better, but ‘Clojure Programming' uses the
>> second possibility. What is the better way and why?
>>
>
-- 
Cecil Westerhof

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Re: How to access record in a hashmap

[Cecil Westerhof]

2014-07-09 17:18 GMT+02:00 Thomas Heller :

> Oh and its rare (outside of macros) to use symbols like that. Usually
> you'd use keywords.
>
> (def object-locations
>   {:whiskey :living-room})
>

​It is from 'Land of Lisp'. The symbols are printed. Or is it possible to
print the keyword without the :?



> On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller  wrote:
>
>> Short and simple answer: NullPointerException
>>
>> (def object-locations nil)
>>
>> (object-locations 'bucket) will throw
>> ('bucket object-locations) => nil
>>
>> HTH,
>> /thomas
>>
>> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>>>
>>> When you have:
>>> (def object-locations {
>>>  'whiskey   'living-room
>>>  'bucket'living-room
>>>  'chain 'garden
>>>  'frog  'garden
>>>  'dummy 'nowhere
>>>  'test  'nowhere
>>>  })
>>>
>>> You can retrieve the location of the bucket with:
>>> (object-locations 'bucket)
>>> and with:
>>> ('bucket object-locations)
>>>
>>> Personally I find the first better, but ‘Clojure Programming' uses the
>>> second possibility. What is the better way and why?
>>>
>>
-- 
Cecil Westerhof

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Re: How to access record in a hashmap

[Timothy Baldridge]

(name :foo)

will return the name as a string

(symbol (name :foo))

Converts the name of the keyword to a symbol


On Wed, Jul 9, 2014 at 9:28 AM, Cecil Westerhof 
wrote:

> 2014-07-09 17:18 GMT+02:00 Thomas Heller :
>
> Oh and its rare (outside of macros) to use symbols like that. Usually
>> you'd use keywords.
>>
>> (def object-locations
>>   {:whiskey :living-room})
>>
>
> ​It is from 'Land of Lisp'. The symbols are printed. Or is it possible to
> print the keyword without the :?
>
>
>
>> On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller 
>> wrote:
>>
>>> Short and simple answer: NullPointerException
>>>
>>> (def object-locations nil)
>>>
>>> (object-locations 'bucket) will throw
>>> ('bucket object-locations) => nil
>>>
>>> HTH,
>>> /thomas
>>>
>>> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:

 When you have:
 (def object-locations {
  'whiskey   'living-room
  'bucket'living-room
  'chain 'garden
  'frog  'garden
  'dummy 'nowhere
  'test  'nowhere
  })

 You can retrieve the location of the bucket with:
 (object-locations 'bucket)
 and with:
 ('bucket object-locations)

 Personally I find the first better, but ‘Clojure Programming' uses the
 second possibility. What is the better way and why?

>>>
> --
> Cecil Westerhof
>
> --
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-- 
“One of the main causes of the fall of the Roman Empire was that–lacking
zero–they had no way to indicate successful termination of their C
programs.”
(Robert Firth)

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Re: How to access record in a hashmap

[Thomas Heller]

Don't know Land of Lisp, but if you print it you can use (name :whiskey) to
get "whiskey" (as a String), also works on (name 'whiskey).


On Wed, Jul 9, 2014 at 5:28 PM, Cecil Westerhof 
wrote:

> 2014-07-09 17:18 GMT+02:00 Thomas Heller :
>
> Oh and its rare (outside of macros) to use symbols like that. Usually
>> you'd use keywords.
>>
>> (def object-locations
>>   {:whiskey :living-room})
>>
>
> ​It is from 'Land of Lisp'. The symbols are printed. Or is it possible to
> print the keyword without the :?
>
>
>
>> On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller 
>> wrote:
>>
>>> Short and simple answer: NullPointerException
>>>
>>> (def object-locations nil)
>>>
>>> (object-locations 'bucket) will throw
>>> ('bucket object-locations) => nil
>>>
>>> HTH,
>>> /thomas
>>>
>>> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:

 When you have:
 (def object-locations {
  'whiskey   'living-room
  'bucket'living-room
  'chain 'garden
  'frog  'garden
  'dummy 'nowhere
  'test  'nowhere
  })

 You can retrieve the location of the bucket with:
 (object-locations 'bucket)
 and with:
 ('bucket object-locations)

 Personally I find the first better, but ‘Clojure Programming' uses the
 second possibility. What is the better way and why?

>>>
> --
> Cecil Westerhof
>
> --
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Re: How to access record in a hashmap

[Cecil Westerhof]

2014-07-09 17:32 GMT+02:00 Timothy Baldridge :

> (name :foo)
>
> will return the name as a string
>
> (symbol (name :foo))
>
> Converts the name of the keyword to a symbol
>

​It is not even necessary. I changed to keywords. The code uses:
`(You see a ~obj on the floor.)

And it is displayed as:
You see a whiskey on the floor.
You see a bucket on the floor.

Maybe it does not work in all cases: so I need to do some testing.
​Let change the rest also to keywords.​



> On Wed, Jul 9, 2014 at 9:28 AM, Cecil Westerhof 
> wrote:
>
>> 2014-07-09 17:18 GMT+02:00 Thomas Heller :
>>
>> Oh and its rare (outside of macros) to use symbols like that. Usually
>>> you'd use keywords.
>>>
>>> (def object-locations
>>>   {:whiskey :living-room})
>>>
>>
>> ​It is from 'Land of Lisp'. The symbols are printed. Or is it possible to
>> print the keyword without the :?
>>
>>
>>
>>> On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller 
>>> wrote:
>>>
 Short and simple answer: NullPointerException

 (def object-locations nil)

 (object-locations 'bucket) will throw
 ('bucket object-locations) => nil

 HTH,
 /thomas

 On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>
> When you have:
> (def object-locations {
>  'whiskey   'living-room
>  'bucket'living-room
>  'chain 'garden
>  'frog  'garden
>  'dummy 'nowhere
>  'test  'nowhere
>  })
>
> You can retrieve the location of the bucket with:
> (object-locations 'bucket)
> and with:
> ('bucket object-locations)
>
> Personally I find the first better, but ‘Clojure Programming' uses the
> second possibility. What is the better way and why?
>

-- 
Cecil Westerhof

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Re: How to access record in a hashmap

[Cecil Westerhof]

2014-07-09 17:50 GMT+02:00 Cecil Westerhof :

> 2014-07-09 17:32 GMT+02:00 Timothy Baldridge :
>
> (name :foo)
>>
>> will return the name as a string
>>
>> (symbol (name :foo))
>>
>> Converts the name of the keyword to a symbol
>>
>
> ​It is not even necessary. I changed to keywords. The code uses:
> `(You see a ~obj on the floor.)
>
> And it is displayed as:
> You see a whiskey on the floor.
> You see a bucket on the floor.
>
> Maybe it does not work in all cases: so I need to do some testing.
> ​Let change the rest also to keywords.​
>

​It seems to work. The only 'problem' is that I​

​need to use:
(pickup :bucket)
instead of:
(pickup 'bucket)​

But that is only temporary, because there will be an optimisation later on.



> On Wed, Jul 9, 2014 at 9:28 AM, Cecil Westerhof 
>> wrote:
>>
>>> 2014-07-09 17:18 GMT+02:00 Thomas Heller :
>>>
>>> Oh and its rare (outside of macros) to use symbols like that. Usually
 you'd use keywords.

 (def object-locations
   {:whiskey :living-room})

>>>
>>> ​It is from 'Land of Lisp'. The symbols are printed. Or is it possible
>>> to print the keyword without the :?
>>>
>>>
>>>
 On Wed, Jul 9, 2014 at 5:03 PM, Thomas Heller 
 wrote:

> Short and simple answer: NullPointerException
>
> (def object-locations nil)
>
> (object-locations 'bucket) will throw
> ('bucket object-locations) => nil
>
> HTH,
> /thomas
>
> On Wednesday, July 9, 2014 3:48:53 PM UTC+2, Cecil Westerhof wrote:
>>
>>  When you have:
>> (def object-locations {
>>  'whiskey   'living-room
>>  'bucket'living-room
>>  'chain 'garden
>>  'frog  'garden
>>  'dummy 'nowhere
>>  'test  'nowhere
>>  })
>>
>> You can retrieve the location of the bucket with:
>> (object-locations 'bucket)
>> and with:
>> ('bucket object-locations)
>>
>> Personally I find the first better, but ‘Clojure Programming' uses
>> the second possibility. What is the better way and why?
>>
>
-- 
Cecil Westerhof

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Re: Land of lisp to Clojure

[John Mastro]

Cecil Westerhof  wrote:
> I read a little about it. And no, I do not use dynamic binding. So I
> probably should use atoms. Is there a convention how to name atoms?

Nope, none that I've come across anyway. Dynamic variables can have very
surprising effects if you're not aware you're dealing with them. This is
more of an issue in Common Lisp than in Clojure because in CL you can
rebind both dynamic and lexical variables with `let`, whereas in Clojure
`let` always produces a lexical binding (`binding` creates dynamic
bindings). With Atoms, the worst that happens is you forget to deref one
and you get an NPE or whatever.

Land of Lisp sounds like a fun book. My "books to read" stack is pretty
massive but I'll get to it eventually.

All the best,

John

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An Averaging function

[Stephen Feyrer]

Hi,

I tried to create the function below in a Lighttable instarepl.  In lieu of
any better idea for formatting, the <  > statements below indicate
instarepl output.

(defn avged ([x]
((def sumed (reduce + x)) < 10 >
(def counted (count x)) < 4 >
(def result (/ sumed counted)) < 5/2 >
result
)))

(avged [1 2 3 4]) < java.lang.ClassCastException: java.lang.Long cannot be
cast to clojure.lang.IFn
Var.java:392 clojure.lang.Var.fn
Var.java:423 clojure.lang.Var.invoke
(Unknown Source) user/avged >

The objective of this function is just a learning exercise.

I have three questions:

1. Why doesn't it work, return a value?

2. What does the error message mean?  and seeing this or similar again, how
do I investigate to get a meaningful Clojure solution?

3.  Code Style, what can I do to improve readability and form?


Thanks.

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Re: An Averaging function

[Sam Ritchie]

About code style, don't do "def"s inside of a function - this binds them 
inside the entire namespace, so your values are escaping and persisting 
when you just want locals. Use "let":


(defn averaged [x]
  (let [summed (reduce + x)
 counted (count x)]
(/ summed counted)))

That function actually does work, by the way. I suspect that farther up 
in your lighttable/repl session you bound "avged" to a number, like (def 
avged 10).

Stephen Feyrer 
July 9, 2014 at 6:48 PM
Hi,

I tried to create the function below in a Lighttable instarepl.  In 
lieu of any better idea for formatting, the < > statements below 
indicate instarepl output.


(defn avged ([x]
((def sumed (reduce + x)) < 10 >
(def counted (count x)) < 4 >
(def result (/ sumed counted)) < 5/2 >
result
)))

(avged [1 2 3 4]) < java.lang.ClassCastException: java.lang.Long 
cannot be cast to clojure.lang.IFn

Var.java:392 clojure.lang.Var.fn
Var.java:423 clojure.lang.Var.invoke
(Unknown Source) user/avged >

The objective of this function is just a learning exercise.

I have three questions:

1. Why doesn't it work, return a value?

2. What does the error message mean?  and seeing this or similar 
again, how do I investigate to get a meaningful Clojure solution?


3.  Code Style, what can I do to improve readability and form?


Thanks.

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703.863.8561
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Twitter // Facebook 



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Re: An Averaging function

[Lee Spector]

On Jul 9, 2014, at 8:48 PM, Stephen Feyrer  wrote:

> Hi,
> 
> I tried to create the function below in a Lighttable instarepl.  In lieu of 
> any better idea for formatting, the <  > statements below indicate instarepl 
> output.
> 
> (defn avged ([x]
> ((def sumed (reduce + x)) < 10 >
> (def counted (count x)) < 4 >
> (def result (/ sumed counted)) < 5/2 >
> result
> )))
> 
> (avged [1 2 3 4]) < java.lang.ClassCastException: java.lang.Long cannot be 
> cast to clojure.lang.IFn
> Var.java:392 clojure.lang.Var.fn
> Var.java:423 clojure.lang.Var.invoke
> (Unknown Source) user/avged >
> 
> The objective of this function is just a learning exercise.
> 
> I have three questions:
> 
> 1. Why doesn't it work, return a value?

Hi Stephen,

The main reason it doesn't work is that the expression after the parameter list 
[x] is a list and will be interpreted as a function call, with the function 
being whatever is returned from the first thing in the list -- which in this 
case is the "def sumed" definition, which returns the defined var.

You could patch (not recommended!) this by adding "do" to the beginning of that 
list:

(defn avged 
  ([x]
(do 
  (def sumed (reduce + x)) 
  (def counted (count x))
  (def result (/ sumed counted)) 
  result)))

That will work, but it's not idiomatic clojure -- it is almost never idiomatic 
clojure to have a def or defn within another defn. Also, you've used the syntax 
that allows for multiple arglist/body pairs, although you only need one so the 
extra layer of parentheses isn't necessary.

Here's how I might write it somewhat more idiomatically:

(defn avged 
 [x]
 (let [sumed (reduce + x)
   counted (count x)
   result (/ sumed counted)]
   result))

=> (avged [1 2 3 4])
5/2
=> (float (avged [1 2 3 4]))
2.5


> 
> 2. What does the error message mean?  and seeing this or similar again, how 
> do I investigate to get a meaningful Clojure solution?

I think it means it's trying to call the value of sumed as a function. I'll 
leave it to others to suggest ways of understanding Clojure error messages (and 
just note for any of those others who have the ability to do something about 
this that it sure would be great to be able to get stack backtraces with values 
of locals regardless of IDE etc.).

> 3.  Code Style, what can I do to improve readability and form?

Myself, I'd probably do it without any variables at all, and name everything 
more meaningfully, e.g.:

(defn average-numbers
  "Returns the average of the provided numbers."
  [numbers]
  (/ (reduce + numbers)
 (count numbers)))

=> (average-numbers [1 2 3 4])
5/2

 -Lee

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Re: An Averaging function

[Lee Spector]

On Jul 9, 2014, at 9:31 PM, Lee Spector  wrote:
> You could patch (not recommended!) this by adding "do" to the beginning of 
> that list:

Or -- I now see, instead of adding the "do" you could just remove the outermost 
parentheses after the parameter list. But as Sam and I said this is a bad way 
to go anyway -- you want to avoid the nested defs.

 -Lee

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