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

[Thomas Heller]

Short and simple answer: NullPointerException

(def object-locations nil)

(object-locations 'bucket) will throw

('bucket object-locations) => nil

HTH,

/thomas

[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})

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[Cecil Westerhof]

2014-07-09 17:03 GMT+02:00 Thomas Heller <th.h...@gmail.com>:

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

[Cecil Westerhof]

2014-07-09 17:18 GMT+02:00 Thomas Heller <th.h...@gmail.com>:

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 <th.h...@gmail.com> 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

[Timothy Baldridge]

(name :foo)

will return the name as a string

(symbol (name :foo))

Converts the name of the keyword to a symbol

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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)

[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).

--

[Cecil Westerhof]

2014-07-09 17:32 GMT+02:00 Timothy Baldridge <tbald...@gmail.com>:

(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.​

--
Cecil Westerhof

[Cecil Westerhof]

2014-07-09 17:50 GMT+02:00 Cecil Westerhof <cldwes...@gmail.com>:

2014-07-09 17:32 GMT+02:00 Timothy Baldridge <tbald...@gmail.com>:

(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.

--
Cecil Westerhof