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Erlson - Erlang Simple Object Notation | ||
====================================== | ||
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Erlson is a dynamic name-value dictionary data type for Erlang. | ||
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Erlson dictionaries come with a convenient syntax and can be directly converted | ||
to and from JSON. | ||
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Examples: | ||
```erlang | ||
% creating an empty dictionary | ||
X = #{}, | ||
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% associating field 'foo' with 1 and 'bar' with "abc" | ||
D = #{foo = 1, bar = "abc"}, | ||
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% accessing dictionary element | ||
1 = D.foo, | ||
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% adding nested dictionaries to dictionary D | ||
D1 = D#{baz = #{fum = #{i = 0}}}, | ||
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% accessing elements of the nested dictionary | ||
0 = D1.baz.fum.i, | ||
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% modifying elements of the nested dictionary | ||
D2 = D1#{baz.fum.i = 100, baz.fum.j = "new nested value"}. | ||
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... | ||
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% converting Erlson dictionary to JSON iolist() | ||
erlson:to_json(D2). | ||
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% creating Erlson dictionary from JSON iolist() | ||
D = erlson:from_json(Json). | ||
''' | ||
General properties | ||
------------------ | ||
* Erlson dictionaries contain zero or more Name->Value associations | ||
(fields), where each Name is `atom()` or `binary()` and Value can be of `any()` | ||
type. | ||
* Name->Value associations are unique. If a new association is created for the | ||
existing Name, the old value will be replaced by the new value. | ||
* Erlson dictionaries can be nested. | ||
Runtime properties | ||
------------------ | ||
* Only fields with `atom()` names can be accessed using the Erlson | ||
dictionary syntax. | ||
* Unlike Erlang records, Erlson dictionaries can be dynamically constructed | ||
without any static type declarations. | ||
* At runtime, Erlson dictionaries are represented as a list of {Name, Value} | ||
tuples ordered by Name. This way, each Erlson dictionary is a valid `proplist` | ||
and `orddict` in terms of the correspondent stdlib modules. | ||
* Erlson dictionaries (dictionary syntax) can't be used as patterns and in | ||
guard expressions. | ||
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* Erlson dicts can be used in both compiled modules and Erlang interactive | ||
shell. | ||
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Properties related to JSON | ||
-------------------------- | ||
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* Each valid JSON object can be converted to correspondent Erlson | ||
dictionary. | ||
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* An Erlson dictionary can be converted to JSON if it follows JSON data | ||
model. | ||
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* JSON->Erlson->JSON conversion produces an equivalent JSON object | ||
(fields will be reordered). | ||
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Usage instructions | ||
------------------ | ||
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For compiled modules that use Erlson syntax, the Erlson library header must be | ||
included: | ||
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-include_lib("erlson/include/erlson.hrl"). | ||
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When rebar is used as a build tool, it should be configured to use | ||
"erlson_rebar_plugin". In order to do that, add the following line to the | ||
project's "rebar.config" file: | ||
{rebar_plugins, [erlson_rebar_plugin]}. | ||
In order to use Erlson syntax from Erlang shell, run the following command (e.g. | ||
include it in `.erlang` file): | ||
erlson:init(). | ||
Dependencies | ||
------------ | ||
Erlson relies on `mochijson2` library for JSON encoding and decoding. It comes | ||
as a part of [Mochiweb](https://github.com/mochi/mochiweb). Erlson doesn't | ||
automatically include it, but if you wish to do it with a rebar-enabled project, | ||
add it as dependency in your `rebar.config`. For example: | ||
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{deps, | ||
[ | ||
% we need Mochiweb for mochijson2 | ||
{mochiweb, "", {git, "https://github.com/mochi/mochiweb.git", {branch, "master"}}} | ||
]}. |